Method for enrichment of heavy component of oxygen isotopes

ABSTRACT

A method and apparatus for enrichment of heavy oxygen isotopes is provided wherein an oxygen starting material which contains heavy oxygen isotopes is enriched in at least one of oxygen molecule  16 O 17 O,  16 O 18 O,  17 O 17 O,  17 O 18 O and  18 O 18 O, by means of cryogenic distillation of the oxygen starting material containing heavy oxygen isotopes. In addition, a method and apparatus are provided for further increasing the concentration of at least one of the heavy isotope oxygen molecules by means of conducting isotope scrambling on the above-mentioned plurality of oxygen molecules enriched by means of the above mentioned cryogenic distillation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for enrichingoxygen in the heavy oxygen isotopes, ¹⁷O and ¹⁸O; and in particular, thepresent invention relates to a method and apparatus for enriching oxygenin these heavy oxygen isotopes by means of cryogenic distillation.

In addition, the present invention relates to a method and apparatus forfurther concentrating heavy oxygen isotopes by means of conductingisotope scrambling following the cryogenic distillation.

This application is based on patent application No. Hei 11-150733 filedin Japan, the content of which is incorporated herein by reference.

2. Background Art

Naturally abundant oxygen comprises 99.759% (atomic %, used in this wayhereinafter) of ¹⁶O, 0.037% of ¹⁷O, and 0.204% of ¹⁸O.

Among these, the heavy isotope ¹⁸O is used as a tracer in fields such asagriculture, biology, and medicine.

In addition, in the same way, since the heavy isotope ¹⁷O has nuclearmagnetic moment, it is used in the research of oxygen compounds usingnuclear magnetic resonance and the like.

As enrichment methods for these heavy oxygen isotopes, there aredistillation, thermal diffusion, chemical exchange (reactions), and thelike. However, as a method of production with low cost and high volume,distillation is generally used. As the distillation method, there aremethods which use water, NO, or CO as the starting material.

Among these method, as those methods whose success has been proven,water distillation methods using water as the starting material, and NOdistillation methods using NO as the starting material can be mentioned.

As a water distillation method; the method practiced by Dostrovsky et alis known, and they reported that using this method it was possible toproduce approximately 6 kg of ¹⁸O of a concentration of 98 to 99% in ayear, and 1.5 kg of ¹⁷O of a concentration of 25% in a year. Inaddition, there are attempts to obtain high concentrations of ¹⁷O bymeans of further enrichment of ¹⁷O obtained by means of this methodusing a thermal diffusion method.

Since NO has a higher relative volatility compared with other startingmaterials, the enrichment efficiency for the above-mentioned isotopes inNO distillation methods is highly advantageous.

This method is used widely for enrichment of the isotopes of nitrogenand, normally, the above-mentioned heavy oxygen isotopes are obtained asbi-products of enrichment of the isotopes of nitrogen.

However, the above-mentioned conventional techniques have the followingproblems.

As shown in Table 1 and Table 2, since heavy isotopes are present inhydrogen and in nitrogen, there is the problem that in theabove-mentioned water distillation methods, enrichment of watercomprising the light isotope of oxygen (¹⁶O) and the heavy isotope ofhydrogen occurs, and in NO distillation methods, enrichment of NOcomprising the light isotope of oxygen (¹⁶O) and the heavy isotope ofnitrogen occurs.

More specifically, in water distillation methods, it is easy for watercontaining the light isotope of oxygen (¹⁶O) and deuterium (HD¹⁶O, etc.)to become mixed into the obtained heavy isotope enriched product. Thishinders enrichment of the H₂ ¹⁷O and H₂ ¹⁸O which contain the heavyisotopes of oxygen, and it is difficult to industrially obtain productwhich is highly enriched in the heavy isotopes of oxygen, such as H₂ ¹⁸Ohaving a purity of 99% or greater. The purity of commercially availableH₂ ¹⁸O is approximately 97%.

TABLE 1 Mass number Water molecule Abundance ratio 18 H₂ ¹⁶O 0.99728 19H₂ ¹⁷O 0.00037 19 HD¹⁶O 0.00031 20 H₂ ¹⁸O 0.00204 20 HD¹⁷O 1.15 × 10⁻⁷ 20 D₂ ¹⁶O 2.43 × 10⁻⁸  21 HD¹⁸O 6.36 × 10⁻⁷  21 D₂ ¹⁷O 9.00 × 10⁻¹² 22D₂ ¹⁸O 4.96 × 10⁻¹¹

TABLE 2 Mass number NO molecule Abundance ratio 30 ¹⁴N⁶⁰O 0.99390 31¹⁴N¹⁷O 0.00037 31 ¹⁵N¹⁶O 0.00369 32 ¹⁴N¹⁸O 0.00203 32 ¹⁵N¹⁷O 1.37 × 10⁻⁶33 ¹⁵N¹⁸O 7.55 × 10⁻⁸

In addition, since the latent heat of vaporization of water iscomparatively high (e.g., approximately six times that of the latentheat of vaporization of oxygen), the water distillation apparatus iscomparatively large and energy consumption is great. For this reason,there is a tendency for water distillation methods to have increasedapparatus and operational costs.

In addition, in NO distillation methods, it is easy for NO (¹⁵N¹⁶O)containing the heavy isotope of nitrogen and oxygen (¹⁶O) to becomemixed into the obtained heavy isotope enriched product, and there is theproblem that it is difficult to obtain an enriched product which ishighly enriched in heavy oxygen isotopes.

In addition, due to reasons such as NO being a corrosive and poisonousgas, there is the problem that the above-mentioned NO distillationmethods require a great deal of expense to put into practice.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems, the method of thepresent invention provides a method of enrichment of heavy oxygenisotopes comprising enriching an oxygen starting material which containsheavy oxygen isotopes in at least one type of oxygen molecule selectedfrom ¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O, ¹⁷O¹⁸O and ¹⁸O¹⁸O, which contain heavyoxygen isotopes, by means of cryogenic distillation of the oxygenstarting material which contains heavy oxygen isotopes.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes comprising enriching an oxygen starting materialwhich contains heavy oxygen isotopes in at least one type of oxygenmolecule selected from ¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O, ¹⁷O¹⁸O and ¹⁸O¹⁸O, whichcontain heavy oxygen isotopes, by means of cryogenic distillation inwhich the oxygen starting material which contains heavy oxygen isotopesis supplied to a distillation column packed with structured packing.

In addition, in the method of enrichment of heavy oxygen isotopes of thepresent invention, as the method for the above-mentioned cryogenicdistillation, a distillation method is used which comprises supplying anoxygen starting material to a distillation column which has been packedwith structured packing; bringing about vapor-liquid contact between adescending liquid and an ascending vapor mainly on the surface of theabove-mentioned structured packing within the above-mentioneddistillation column; at which time, the liquid and the vapor flow inmutually opposite directions over the surface of the above-mentionedstructured packing along the main flow direction, which is along thedirection of the column axis, and at the same time mixing of the liquidand/or the vapor in a direction at right angles to the above-mentionedmain flow direction is promoted and mass transfer occurs.

In addition, according to the present invention, it is preferable toperform the aforementioned cryogenic distillation of oxygen such thatthe density corrected superficial velocity (the superficial F factor) isat least 0.5 m/s(kg/m³)^(½) and no greater than 2.0 m/s(kg/m³)^(½) andmore preferably, at least 0.8 m/s(kg/m³)^(½) and no greater than 1.8m/s(kg/m³)^(½).

In addition, according to the present invention, it is preferable toperform the aforementioned cryogenic distillation of oxygen such thatthe distillation pressure is in the range of 0.5 bar to 5 bar, and morepreferably, 1.1 bar to 2.5 bar.

As the oxygen starting material, it is preferable to use highly pureoxygen having a purity of 99.999% or greater. In particular, it ispreferable to use cryogenically manufactured high purity oxygen obtainedfrom a high purity oxygen preparation device using cryogenicdistillation.

In addition, the method of the present invention is a method forenrichment of heavy oxygen isotopes comprising using a distillationcolumn comprising three distillation columns, a first column, a secondcolumn and a third column, as the above-mentioned distillation column;supplying an oxygen starting material from a feed section to the firstcolumn; supplying at least a part of the liquid or vapor output from thebottom of the first column to the second column; supplying at least apart of the liquid or vapor output from the second column to the thirdcolumn; and extracting an enriched vapor having a concentration of¹⁶O¹⁷O of 10% or greater from the top of the third column.

In addition, the method of the present invention is a method ofenrichment of heavy oxygen isotopes comprising carrying out thedistillation in such a way that in the second column a concentrationpeak of ¹⁶O¹⁷O is created at the middle of the column, and that amixture of heavy oxygen isotopes comprising ¹⁶O¹⁷O at a concentration of1% or greater, ¹⁶O¹⁸O at a concentration of 90% or greater, and theremainder being mostly ¹⁶O¹⁶O is separated at the bottom of the secondcolumn.

In addition, the method of the present invention is a method ofenrichment of heavy oxygen isotopes comprising carrying out thedistillation such that enriched liquid or vapor having a concentrationof ¹⁶O¹⁸O of 90% or greater is separated at the bottom of the thirdcolumn.

In addition, the method of the present invention is a method in whichthe distillation column is equipped with a condenser for cooling andliquefying vapor output from the distillation column, and a reboiler forheating and vaporizing the liquid output from the distillation column,and a medium for heat exchange for exchanging heat with the output vaporand the output liquid in the condenser and the reboiler, wherein atleast one gas selected from nitrogen, oxygen, air, and the exhaust gasof an air separation unit is used as the medium for heat exchange.

In addition, it is preferable if a structure comprising a plurality ofdistillations columns is used as the above-mentioned distillationcolumn.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes comprising enrichment of at least one type ofoxygen molecule selected from among ¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O, ¹⁷O¹⁸O and¹⁸O¹⁸O, which contain heavy oxygen isotopes, by means of performingcryogenic distillation of an oxygen starting material containing heavyoxygen isotopes; subsequently conducting isotope scrambling; andobtaining an enriched product comprising a high concentration of atleast one type of oxygen molecule containing the above-mentioned heavyoxygen isotopes.

The above-mentioned “isotope scrambling” is a general term describingthe phenomena where in the presence of a plurality of molecularisotopes, each molecule randomly exchanges atoms with the othermolecules. The “isotope exchange” using a catalyst described below is atypical example of this.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein an enriched product comprising an evenhigher concentration of at least one type of oxygen molecule containingsaid heavy oxygen isotopes is obtained by means of performing repeatcryogenic distillation on a heavy oxygen isotope enriched materialobtained by means of the above-mentioned isotope scrambling.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein the concentration of:at least onecomponent of a heavy oxygen isotope enriched material, obtained by meansof the aforementioned method of enrichment of heavy oxygen isotopes, isincreased by means of conducting additional isotope scrambling.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein the concentration of at least the heavyisotope oxygen ¹⁸O¹⁸O is further increased by means of performing repeatcryogenic distillation on the heavy oxygen isotope enriched materialobtained by means of the aforementioned method.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein a heavy oxygen isotope enriched materialcontaining an increased concentration of the heavy isotope oxygen¹⁸O¹⁸O, and an enriched product containing an increased concentration ofthe heavy oxygen isotope ¹⁷O are obtained by means of performing furthercryogenic distillation on a heavy oxygen isotope enriched materialobtained by means of the aforementioned method.

In addition, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein a plurality of distillation columns areused and operated such that the maximum concentration of ¹⁷O¹⁸O appearsin the middle section within the penultimate (next-to-last) distillationcolumn, at the time of carrying out the enrichment of oxygen moleculescontaining heavy oxygen isotopes by means of performing theaforementioned cryogenic distillation.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein the aforementioned isotope scrambling forconcentrating the above-mentioned heavy oxygen isotopes comprisesisotope exchange using a catalytic reaction.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein the aforementioned: isotope scrambling forconcentrating the above-mentioned heavy oxygen isotopes comprises addinghydrogen to and reacting it with the above-mentioned heavy oxygenisotope enriched material to produce water containing a highconcentration of the above-mentioned heavy oxygen isotopes; andsubsequently conducting electrolysis of said produced water to separateit into oxygen containing heavy oxygen isotopes and hydrogen.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein the aforementioned isotope scrambling forconcentrating the heavy oxygen isotopes comprises passing theabove-mentioned heavy oxygen isotope enriched material through plasma bymeans of silent discharge, high-frequency discharge, or electromagneticinduction.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein the aforementioned isotope scrambling forconcentrating the heavy oxygen isotopes comprises irradiating theabove-mentioned heavy oxygen isotope enriched material with ultravioletrays to form ozone from said enriched material, and then decomposing theozone.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein the aforementioned isotope scrambling forconcentrating the heavy oxygen isotopes is carded out by means of anoxidation-reduction reaction of the above-mentioned heavy oxygen isotopeenriched material with BaO, SrO, CaO, Cu₂O, FeO, CO, Mn₃O₄, Ag, Au,and/or a mixture thereof.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein the aforementioned isotope scrambling forconcentrating the heavy oxygen isotopes comprises isotope exchange inwhich the above-mentioned heavy oxygen isotope enriched material isthermally treated at a temperature of 1000° C. or higher.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein the above-mentioned reaction between theabove-mentioned enriched material and hydrogen is conducted by means ofcombustion using a combustion chamber.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein the above-mentioned reaction between theabove-mentioned enriched material and hydrogen is a catalytic reactionin which an inert gas such as Ar is supplied to said reaction system asa diluent gas to dilute the above-mentioned enriched material andhydrogen.

In addition, according to the present invention, examples of thecatalyst used for catalytic reaction of the above-mentioned enrichedmaterial and the above-mentioned hydrogen may include a catalystcontaining at least one component selected from the group comprising Pd,Pt, Rh, Ru, Ni, Cu, Au, Mn and metal oxides thereof

Furthermore, it is possible to use at least one type of catalyst inwhich these metals or metal oxides (Pt, Pd, Rh, etc.) are carried byAl-oxide, Si-oxide, Ti-oxide, Zr-oxide, Cr-oxide, V-oxide, Co-oxide,Mn-oxide, and the like.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein water produced by means of reacting theabove-mentioned enriched material with hydrogen is cooled and condensed;said condensed water is separated from the diluent gas; and the diluentgas separated from the condensed water is returned to theabove-mentioned reaction system for recirculation and reuse.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein hydrogen produced by means of theabove-mentioned electrolysis is recycled and reused as hydrogen foraddition to the above-mentioned enriched material.

Additionally, the present invention provides a method of enrichment ofheavy oxygen isotopes wherein impurities in oxygen produced by means ofthe above-mentioned electrolysis are removed through oxidization bymeans of a catalytic reaction.

As the catalyst used for said catalytic reaction, a catalyst comprisingat least one component selected from among the group comprising Pt, Pd,Rh, Ru, Au, Ni, Cu, and Ag—Pd is suitable.

Further, more preferred examples include at least one type of catalystwherein these metals (Pt, Pd, Rh, etc.) are carried by one of theaforementioned metallic oxides (Al-oxide, Si-oxide, etc.).

The apparatus used in the present invention is an apparatus for theenrichment of heavy oxygen isotopes which comprises a distillationcolumn packed with structured packing and is an apparatus for enrichingat least one type of oxygen molecule selected from among ¹⁶O¹⁷O, ¹⁶O¹⁸O,¹⁷O¹⁷O, ¹⁷O¹⁸O and ¹⁸O¹⁸O which contain heavy oxygen isotopes by meansof cryogenic distillation of oxygen.

In the same way, in the apparatus for the enrichment of heavy oxygenisotopes of the present invention, the above-mentioned structuredpacking is promoting-fluid-dispersion type structured packing which hasa structure such that when a liquid descending in the distillationcolumn and a vapor ascending in the distillation column make contact,the liquid and the vapor flow in mutually opposite directions over thesurface of the above-mentioned structured packing along the main flowdirection, which is along the direction of the column axis, and at thesame time mixing of the liquid and/or the vapor in a direction at rightangles to the above-mentioned main flow direction is promoted and masstransfer occurs.

In addition, in the apparatus for the enrichment of heavy oxygenisotopes of the present invention, the specific surface area of thepacking in the above-mentioned distillation column is in the range of350 m²/m³ to 1200 m²/m³, and preferably 500 m²/m³ to 750 m²/m³.

The apparatus for the enrichment of heavy oxygen isotopes of the presentinvention comprises at least one distillation column for enriching atleast one type of oxygen molecule selected from among ¹⁶O¹⁷O, ¹⁶O¹⁸O,¹⁷O¹⁷O, ¹⁷O¹⁸O and ¹⁸O¹⁸O, which contain heavy oxygen isotopes, by meansof cryogenic distillation of an oxygen starting material containingheavy oxygen isotopes; and at least one isotope scrambler for increasingthe concentration of at least one type of oxygen molecule selected fromamong ¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O, ¹⁷O¹⁸O and ¹⁸O¹⁸O, which contain heavyoxygen isotopes, in the heavy oxygen isotope enriched material obtainedfrom the above-mentioned distillation column, by means of isotopescrambling.

Additionally, in the apparatus for the enrichment of heavy oxygenisotopes of the present invention, the above-mentioned isotope scrambleris provided with an isotope exchange catalyst for the promotion ofisotope exchange in the above-mentioned enriched material, and thisisotope exchange catalyst includes at least one constituent selectedfrom among the group comprising W, Ta, Pd, Rh, Pt and Au.

Additionally, in the apparatus for the enrichment of heavy oxygenisotopes of the present invention, the above-mentioned isotope scrambleris provided with an isotope exchange catalyst for the promotion ofisotope exchange in the above-mentioned enriched material, and thisisotope exchange catalyst includes at least one constituent selectedfrom among the group comprising Ti-oxide, Zr-oxide, Cr-oxide, Mn-oxide,Fe-oxide, Co-oxide, Ni-oxide, Cu-oxide, Al-oxide, Si-oxide, Sn-oxide,and V-oxide.

In addition, in the apparatus for the enrichment of heavy oxygenisotopes according to the present invention, the distillation column ispacked with structured packing, and the above-mentioned structuredpacking is promoting-fluid-dispersion type structured packing which hasa structure such that when a liquid descending in the distillationcolumn and a vapor ascending in the distillation column make contact,the liquid and the vapor flow in mutually opposite directions over thesurface of the above-mentioned structured packing along the main flowdirection, which is along the direction. of the column axis, and at thesame time mixing of the liquid and/or the vapor in a direction at rightangles to the above-mentioned main flow direction is promoted and masstransfer occurs.

In addition, in the apparatus of the present invention, the specificsurface area of the packing in the above-mentioned distillation columnmay be in the range of 350 m²/m³ to 1200 m²/m³, and preferably 500 m²/m³to 750 m²/m³.

Additionally, in the apparatus of the present invention, theabove-mentioned distillation column may comprise a plurality (n) ofdistillation columns (A_(l)˜A_(n)), wherein the bottoms of the columnsA_(k) (k: a natural number of (n−1) or less) are connected to the topsof columns A_(k+1) by a conduit pipe via a liquid transfer means whichsends liquid output from column A_(k) to column A_(k+1), and the lowerpart of the column A_(k) is connected to the top of column A_(k+1) by aconduit pipe for transferring the vapor output from the column A_(k+1)to the column A_(k).

Additionally, in the apparatus of the present invention, a condenser ispreferably provided at the top of the aforementioned column A₁, and areboiler is preferably provided at the bottom of the aforementionedcolumn A_(k+1).

Additionally, in the present invention, a circulation system for amedium for heat exchange which connects a second conduit of theabove-mentioned condenser and a second conduit of the above-mentionedreboiler may be provided, and a circulation means for circulating themedium for heat exchange (for example, air, nitrogen, oxygen, or thelike) may be provided somewhere along the above-mentioned circulationsystem.

The aforementioned circulation means may comprise a low-temperaturecompressor.

In addition, the aforementioned circulation means may comprise a normaltemperature compressor. In this case, a heat exchanger for conductingheat exchange between the medium for heat exchange at the inlet of theabove-mentioned normal temperature compressor and the medium for heatexchange at the outlet of the above-mentioned normal temperaturecompressor is preferably provided.

In addition, in the apparatus of the present invention, a plate fin typecondenser maybe provided at the top of the above-mentioned distillationcolumn, and a coil-type reboiler or a plate fin type reboiler may beprovided within the above-mentioned column in the vicinity of thebottom. In addition, a conduit pipe is connected to the inlet side of afirst conduit of the above-mentioned condenser for introducing at leasta part of the output vapor from the top of the distillation column intothe above-mentioned first conduit of the above-mentioned condenser. Aconduit pipe is connected to the outlet side of the first conduit forintroducing liquid output from this conduit into the top of theabove-mentioned distillation column again. A conduit pipe forcirculating a medium for heat exchange is connected to the secondconduit of the condenser, this conduit pipe for circulating a medium forheat exchange is connected to the above-mentioned coil type reboiler orplate fin type reboiler, and a circulation means is provided in theabove-mentioned conduit pipe for circulating the medium for heatexchange within the above-mentioned conduit pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a structural outline of an embodiment of anapparatus for the enrichment of heavy oxygen isotopes of the presentinvention.

FIG. 2 is a perspective view showing an example of thenon-promoting-fluid-dispersion type structured packing which can be usedin the enrichment apparatus shown in FIG. 1.

FIG. 3 is a perspective view showing another example of thenon-promoting-fluid-dispersion type structured packing which can be usedin the enrichment apparatus shown in FIG. 1.

FIG. 4 is a perspective view showing an example of thepromoting-fluid-dispersion type structured packing which can be used inthe enrichment apparatus shown in FIG. 1.

FIG. 5 is a perspective view showing another example of thepromoting-fluid-dispersion type structured packing which can be used inthe enrichment apparatus shown in FIG. 1.

FIG. 6 is a perspective view showing another example of thepromoting-fluid-dispersion type structured packing which can be used inthe enrichment apparatus shown in FIG. 1.

FIG. 7 is a graph showing the simulated results for a distillationoperation as an example of when the enrichment apparatus shown in FIG. 1is used.

FIG. 8 is a graph showing the simulated results for a distillationoperation as an example of when the enrichment apparatus shown in FIG. 1is used.

FIG. 9 is a diagram showing a structural outline of another embodimentof the apparatus for the enrichment of heavy oxygen isotopes of thepresent invention.

FIG. 10 is a diagram showing a structural outline of an example of adistillation column which can be used in the apparatus for theenrichment of heavy oxygen isotopes of the present invention.

FIG. 11 is a diagram showing a structural outline of yet anotherembodiment of the apparatus for the enrichment of heavy oxygen isotopesof the present invention.

FIG. 12 is a diagram showing a structural outline of yet anotherembodiment of the apparatus for the enrichment of heavy oxygen isotopesof the present invention.

FIG. 13 is a graph showing the simulated results of the distillationoperation as an example of when the enrichment apparatus shown in FIG. 9is used, and shows the concentration distribution of each of theisotopes within the first distillation column.

FIG. 14 is a graph showing the simulated results of the distillationoperation as an example of when the enrichment apparatus shown in FIG. 9is used, and shows the concentration distribution of each of theisotopes within the second distillation column.

FIG. 15 is a graph showing the simulated results of the distillationoperation as an example of when the enrichment apparatus shown in FIG. 9is used, and shows the concentration distribution of each of theisotopes within the third distillation column.

FIG. 16 is a diagram showing a structural outline of yet anotherembodiment of the apparatus for the enrichment of heavy oxygen isotopesof the present invention.

FIG. 17 is a diagram showing a structural outline of yet anotherembodiment of the apparatus for the enrichment of heavy oxygen isotopesof the present invention.

FIG. 18 is a diagram showing a structural outline of yet anotherembodiment of the apparatus for the enrichment of heavy oxygen isotopesof the present invention.

FIG. 19 is a structural outline showing an example of an isotopescrambler used in the enrichment apparatus of the present invention.

FIG. 20 is a structural outline showing the main parts of anotherexample of an isotope scrambler used in the apparatus for the enrichmentof heavy oxygen isotopes of the present invention.

FIG. 21 is a graph showing the simulated results of the concentrationsof the heavy oxygen isotopes for an example in which the apparatus shownin FIG. 17 was used, and shows the concentration distribution of eachisotope within the first distillation column.

FIG. 22 is a graph showing the simulated results of the concentrationsof the heavy oxygen isotopes for an example in which the apparatus shownin FIG. 17 was used, and shows the concentration distribution of eachisotope within the second distillation column.

FIG. 23 is a graph showing the simulated results of the concentrationsof the heavy oxygen isotopes for an example in which the apparatus shownin FIG. 17 was used, and shows the concentration distribution of eachisotope within the third distillation column.

FIG. 24 is a graph showing the simulated results of the concentrationsof the heavy oxygen isotopes for an example in which the apparatus shownin FIG. 18 was used, and shows the concentration distribution of eachisotope within the first distillation column.

FIG. 25 is a graph showing the simulated results of the concentrationsof the heavy oxygen isotopes for an example in which the apparatus shownin FIG. 18 was used, and shows the concentration distribution of eachisotope within the second distillation column.

FIG. 26 is a graph showing the simulated results of the concentrationsof the heavy oxygen isotopes for an example in which the apparatus shownin FIG. 18 was used, and shows the concentration distribution of eachisotope within the third distillation column.

FIG. 27 is a graph showing the simulated results of the concentrationsof the heavy oxygen isotopes for an example in which the apparatus shownin FIG. 18 was used, and shows the concentration distribution of eachisotope within the fourth distillation column.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a diagram showing an embodiment of an apparatus for theenrichment of heavy oxygen isotopes according to an embodiment of thepresent invention. The enrichment apparatus shown comprises a firstdistillation column 11 which is a packed column packed with structuredpacking 14 and 15; a condenser 12 for cooling and liquefying at least apart of the vapor (output vapor) output from the top of distillationcolumn 11; a reboiler 13 for heating and vaporizing at least a part ofthe liquid (output liquid) output from the bottom of the distillationcolumn 11; a storage tank 18 for a medium for heat exchange forexchanging heat with the above-mentioned output vapor and theabove-mentioned output liquid within the condenser 12 and the reboiler13; a circulation system 19 for circulating said medium for heatexchange passed the condenser 12 and the reboiler 13; a blower(compressor) 16 which is a ventilating (circulating) means forcirculating the medium for heat exchange within the circulation system19; and a heat exchanger 17 for the medium for heat exchange.

The lower part of the distillation column 11 is packed with structuredpacking 14, and the upper part of distillation column 11 is packed withstructured packing 15.

As the structured packing 14 and 15, it is possible to suitably usenon-promoting-fluid-dispersion type structured packing and/orpromoting-fluid-dispersion type structured packing.Non-promoting-fluid-dispersion type structured packing has a shape andstructure with which the liquid descending within the distillationcolumn and the vapor ascending within the distillation column flow inopposition to one another along the surface of the packing, andvapor-liquid contact occurs without the promotion of mixing of theliquid and vapor in the horizontal cross-section direction with respectto the column axis. As examples, a packing material in which a largenumber of plates formed from aluminum, copper, alloy of aluminum andcopper, stainless steel, various types of plastic, or the like arepositioned parallel to the direction of the main flow (the direction ofthe column axis) can be mentioned.

Here, the main flow indicates the descending liquid and the ascendingvapor which occurs along the direction of the column axis within thedistillation column, therefore, it indicates the flow in the directionof the column axis with respect to the flow of mass transfer which isproduced at the liquid-vapor interface (in other words, the boundarylayer) at the surface of the packing.

Examples of typical non-promoting-fluid-dispersion type packingmaterials are shown in FIG. 2 and FIG. 3.

FIG. 2 is FIG. 7 disclosed in Japanese Utility Model Application, FirstPublication No. Sho 56-20624; and FIG. 3 is FIG. 4 disclosed in JapaneseUtility Model Application, First Publication No. Sho 51-45935.

The non-promoting-fluid-dispersion type structured packing 51 shown inFIG. 2 has a honeycomb structure comprising plates parallel to thedirection of the axis of the column.

In addition, the non-promoting-fluid-dispersion type structured packing52 shown in FIG. 3 is a lattice structure comprising a plurality ofmutually parallel plates 52 a and a plurality plates 52 b which arearranged at right angles with respect to the plates 52 a, and thislattice structure is positioned along the direction of the column axis.

Promoting-fluid-dispersion type structured packing has a shape andstructure with which vapor-liquid contact occurs mainly on the surfaceof the above-mentioned structured packing between the liquid descendingwithin the distillation column and the vapor ascending within thecolumn, at which time, the liquid and the vapor flow in opposition toone another on the surface of the above-mentioned structured packing inthe direction of the main flow which is along the direction of thecolumn axis, and at the same time, mixing of the liquid and/or the vaporin a direction at right angles to the above-mentioned main flowdirection is promoted and vapor-liquid contact occurs. These are calledstructured packing or regular packing in which thin plates of aluminum,copper, aluminum-copper alloy, stainless steel, various plastics, or thelike are formed into a variety of regular forms, and then made into alaminated block.

Typical examples of promoting-fluid-dispersion type structured packingare shown in FIG. 4, FIG. 5 and FIG. 6. The example shown in FIG. 4 isFIG. 3 disclosed in Japanese Examined Patent Application, SecondPublication No. Sho 57-36009. The example shown in FIG. 5 is FIG. 1disclosed in Japanese Unexamined Patent Application, First PublicationNo. Sho 54-16761. The example shown in FIG. 6 is FIG. 3 disclosed inJapanese Unexamined Patent Application, First Publication No. Sho54-15554.

All of the examples shown in these figures show the form of awave-shaped thin plate which is a structural component of this type ofpacking. Small holes (references 53 a, 54 a, and 55 a in the figures)having a diameter of 2˜4 mm are punched in a thin plate of metal such asaluminum having a thickness of 0.1˜0.3 mm with a fixed regulardistribution, which is then molded into a wave shape.

In the promoting-fluid-dispersion type structured packing 53 shown inFIG. 4, a plurality of wave-shaped thin plates are disposed parallel tothe column axis and made into the form of a block by layering the platesso that they come into contact with one another. The wave-shaped groovesin each of the thin plates are inclined with respect to the column axis,and neighboring wave-shaped thin plates are disposed so that thedirection of their wave-shaped grooves intersect one another. Inaddition, a plurality of holes 53 a are provided in the thin plates.When the thin plates are disposed perpendicular with respect to thehorizontal plane, the holes are provided with an interval of spacingtherebetween and form a plurality of rows along a direction which is atright angles to the column axis. In the promoting-fluid-dispersion typestructured packing 53 having this type of structure, the extent of thepacking's ability to promote fluid distribution will vary depending onthe size and number of holes 53 a, the distribution of the plurality ofholes 53 a provided in the wave-shaped thin plates, and the like.Accordingly, many inventions have been proposed which are characterizedby the selection and combination of these conditions.

FIG. 5 shows an example of a structural unit of anotherpromoting-fluid-dispersion type structured packing. In thepromoting-fluid-dispersion type structured packing 54 shown here, a thinplate is molded pressed in a wave shape to form wave-shaped grooves. Inaddition, this example, has the feature that extremely small wave-shapedgrooves 54 b are formed in the thin plates at a fixed angle with respectto the wave-shaped grooves.

It is preferable for the direction in which the wave-shaped grooves areformed to be set within the range of 15˜60° with respect to the columnaxis, and for the direction in which the extremely small wave-shapedgrooves 54 b are formed to be set within the range of 15˜90° withrespect to the column axis. In addition, it is preferable for the lengthand height of the extremely small wave-shaped grooves 54 b to be 0.3 to3 mm. In addition, reference 54 a indicates holes formed in the thinplate.

The promoting-fluid-dispersion type structured packing 55 shown in FIG.6 has the feature of having a structure in which sections havingextremely small grooves formed at a fixed angle with respect to thewave-shaped grooves and smooth sections which do not have theseextremely small grooves are provided alternately in the wave-shaped thinplate. In addition, the reference 55 a indicates holes formed in thethin plates.

In addition, when blocks of these promoting-fluid-dispersion typestructured packing are packed in the distillation column, it ispreferable to carry out the stacking by rotating the loading angle forthe block in the column cross-section (i.e., the angle for disposing thewave-shaped thin plates) by a fixed angle for each block or each set ofblocks, and thereby, the effect of achieving uniform dispersion is evenfurther improved.

The detailed shape and structure of each of the various packings, theircharacteristics, and the characteristics of the packing method areintroduced in Japanese Unexamined Patent Application, First Publication,No. Sho 58-26997, for example, as well as in the three references citedabove.

In the present invention, of the two types of structured packing(non-promoting-fluid-dispersion type structured packing andpromoting-fluid-dispersion type structured packing), it is particularlypreferable to use promoting-fluid-dispersion type structured packing.

This is because when promoting-fluid-dispersion type structured packingis used, the flow of the descending liquid and the ascending vaporwithin the column readily becomes uniform, and it is possible toincrease the efficiency of the vapor-liquid contact.

In addition, it is preferable for the specific surface area of theabove-mentioned packing to be 350 m²/m³ to 1200 m²/m³, and morepreferably 500 m²/m³ and 750 m²/m³. When the specific surface area isless than 350 m²/m³, the vapor-liquid contact surface area isinsufficient and the efficiency of the vapor-liquid contact is reduced.When the specific surface area exceeds 1200 m²/m³, there is concern thatflooding will occur.

In addition, in order for the vapor-liquid contact to proceedefficiently in the distillation column 11, it is preferable to provideat least one collector and one distributor (not shown in the Figures) inthe distillation column 11.

Condenser 12 has a first conduit 12 a into which vapor output from thetop of distillation column 11 is introduced, and a second conduit 12 bthrough which a medium for heat exchange passes for heat exchange withthe vapor within the first conduit 12 a, and is made such that theabove-mentioned output vapor can be cooled and liquefied by means ofheat exchange with the medium for heat exchange. As condenser 12, it ispreferable to use plate fin type heat exchangers of counter current typeor parallel flow type. In particular, since the amount of the medium forheat exchange required for distillation is small, it is preferable forthe condenser to be a non-submerged type which is provided outside ofthe distillation column 11.

The reboiler 13 has a first conduit 13 a into which liquid output fromthe distillation column 11 is introduced, and a second conduit 13 bthrough which the medium for heat exchange passes for heat exchange withthe liquid within the first conduit 13 a, and is made such that theabove-mentioned output liquid can be heated and vaporized by means ofheat exchange with the medium for heat exchange.

As the reboiler 13, it is preferable to use plate fin type heatexchanger of counter current type or parallel flow type.

In this case, the reboiler 13 may be installed outside or inside thedistillation columns 11, but for the purpose of easy manufacture, it ispreferable for the reboiler 13 to be installed outside.

In addition, in place of the reboiler 13, it is possible to install acoil type reboiler within the bottom of the distillation column. Thissituation is advantageous from the point of view of the amount of liquidrequired for the liquid at bottom of the column, however, it isdisadvantageous form the point of view of the surface area for heatexchange, and manufacturing efficiency.

As a blower 16, an normal temperature compressor can be used.

In addition, heat exchanger 17 a first conduit 17 a into which themedium for heat exchange which has passed through the second conduit 12b of the above-mentioned condenser 12 is introduced, and a secondconduit 17 b into which the medium for heat exchange which has passedthrough blower 16 is introduced, and is made such that heat exchange canoccur between the medium for heat exchange within the first conduit 17 aon the inlet side of the blower 16 and the medium for heat exchangewithin the second conduit 17 b on the outlet side of the blower 16. Asthe heat exchanger 17, it is preferable to use a counter-flow type or aparallel-flow type plate-fin heat exchanger.

In the following, as an example in which the above-mentioned apparatusis used, an example of a method for enrichment of ¹⁶O¹⁷O and ¹⁶O¹⁸O ofthose oxygen molecules which contain heavy oxygen isotopes is explained.

Initially, an oxygen vapor starting material (feed 101) is supplied tothe distillation column 11, via the conduit pipe 20 which serves as afeeding section connected to the first distillation column 11 at aposition intermediate between the bottom section packed with packing 14and the upper section packed with packing 15.

The use of oxygen with high purity is preferred as the aforementionedoxygen vapor starting material. As methods for producing oxygen of highpurity, known methods which use production apparatus for oxygen withhigh purity can be used, such as methods disclosed in Japanese ExaminedPatent Application, Second Publication No. Hei 4-13628; JapaneseUnexamined Patent Application, First Publication No. Sho 64-41748;Japanese Unexamined Patent Application, First Publication No. Sho64-46563; Japanese Unexamined Patent Application, First Publication No.Hei 3-17488, and Japanese Examined Patent Application, SecondPublication No. Hei 6-72740.

As the above-mentioned oxygen of high purity, it is preferable to useoxygen with a purity of 99.999% or higher, from which impurities such asargon, hydrocarbons, krypton, xenon, and fluorine compounds (such asperfluorocarbons) have been removed in advance.

By means of the use of oxygen of high purity, there are no componentswhich hinder the enrichment of oxygen in the heavy oxygen isotopesaccording to each of the processes of the present invention, and each ofthe processes proceeds well. In particular, the use of an oxygenstarting material from which hydrocarbons have been removed ispreferable from the point of view of safety.

In addition, it is preferable to use a cryogenic high purity oxygenproduct obtained from a production apparatus for oxygen with high purityusing cryogenic distillation, because the oxygen starting material canbe used as a cooling source. Moreover, as the oxygen starting material,it is also possible to use liquefied oxygen.

The oxygen starting material; vapor supplied to the distillation column11 is distilled by means of vapor-liquid contact with a reflux liquid(i.e., descending liquid) described below, when ascending within thedistillation column 11 and passing through the packing 15.

In this process, those molecules in the oxygen starting material vaporwhich contain heavy oxygen isotopes (i.e. ¹⁶O¹⁷O, ¹⁶O¹⁸O, etc.) are morelikely to condense due to their high boiling points, and the condensedliquid flows down with the reflux liquid within the distillation column11 as the descending liquid.

Accordingly, oxygen vapor (¹⁶O¹⁶O enriched vapor), having a decreasedconcentration of the heavy isotopes, separates at the top of thedistillation column 11.

The enriched vapor is then output from the distillation column 11 viathe conduit pipe 21, and a portion of the vapor is introduced viaconduit pipe 23 into the first conduit 12 a of the condenser 12, whereit is condensed by means of heat exchange with the medium for heatexchange flowing within the second conduit 12 b, and returned to the topof the distillation column 11 via conduit pipe 24 as a reflux liquid104.

The remaining portion of the aforementioned enriched vapor output fromthe distillation column 11 via the conduit pipe 21 is discharged out ofthe system as exhaust vapor 105 via the conduit pipe 22.

The reflux liquid introduced into the top of the distillation column 11flows down as descending liquid while making vapor-liquid contact withthe oxygen starting material vapor which is ascending within thedistillation column 11, and reaches the bottom of the distillationcolumn 11. In this process of vapor-liquid contact, the descendingliquid becomes enriched in heavy oxygen isotopes, which have a greatertendency to liquefy.

Liquid which accumulates at the bottom of the distillation column 11(hereinafter, referred to as the “column bottom liquid”) is output fromthe distillation column 11 and introduced into the first conduit 13 a ofthe reboiler 13 via the conduit pipe 25, where it is vaporized by meansof heat exchange with the medium for heat exchange flowing within thesecond conduit 13 b. Subsequently, it is output from the reboiler 13 viaconduit pipe 26, and a portion thereof (reboiler vapor 103) isreintroduced into the bottom of the distillation column 11 via conduitpipe 27 and becomes; ascending vapor which rises within the distillationcolumn 11.

The remaining portion of the vapor output from the first conduit 13 a ofthe reboiler 13 is discharged from the system via conduit pipe 28 asproduct vapor 102 enriched in heavy oxygen isotopes.

Next, the flow of the medium for heat exchange which passes through thesecond conduit 12 b of the condenser 12 and the second conduit 13 b ofthe reboiler 13 will be explained.

As the medium for heat exchange, it is possible to use at least one ofnitrogen, oxygen, air or the exhaust gas of an air separation unit. Inthe following, an example in which nitrogen is used as the medium forheat exchange will be explained.

Nitrogen within a storage tank 18, which has been filled with liquidnitrogen in advance, is output from the storage tank 18 through pipe 29in a gaseous state as the medium for heat exchange, it passes throughvalve 30 and pipes 31 and 32 and flows into the second conduit 13 b ofthe reboiler 13, and exchanges heat with the column bottom liquid(oxygen) within the first conduit 13 a.

The nitrogen which has passed through the reboiler 13 then passes alongpipe 33 and the pressure is reduced at the valve 34 and, at this time, apart thereof condenses.

Next, this nitrogen passes along pipe 35, flows into second conduit 12 bof the condenser 12, and exchanges heat with the oxygen vapor within thefirst conduit 12 a, and is vaporized.

The vaporized nitrogen passes along pipes 36 and 40 and is introducedinto the first conduit 17 a of the heat exchanger 17, and here it isheated to normal temperature through heat exchange with the nitrogenwithin the second conduit 17 b, then it is introduced into the blower16, and is pressurized.

The nitrogen pressurized by the blower 16 is introduced into secondconduit 17 b of heat exchanger 17, where it exchanges heat with thenitrogen within the first conduit 17 a and is cooled, then it passesalong pipe 43, is introduced into the above-mentioned pipe 31, andcirculates through the above-described path.

The above-described circulation system 19 is a course comprising conduitpipes 31, 32, 33, 35, 36, 40, 41, 42, and 43 which are circulationconduit pipes for circulation nitrogen as the medium for heat exchangebetween the condenser 12 and the reboiler 13.

In the above-described method, it is possible to introduce the liquidnitrogen within the storage tank 18, for example, into theabove-mentioned conduit pipe 35 via conduit pipe 45 which has valve 44and supply it to the apparatus as a cooling source.

In addition, it is possible for a part of the circulating nitrogen to bedischarged out of the system through conduit pipes 37 and 39 which areequipped with valve 38.

In this way, by means of the use and circulation of the medium for heatexchange, it is possible to utilize the cool temperature of the mediumfor heat exchange without waste and to reduce energy loss to a minimum,and thus to reduce operating costs.

In the above-mentioned operation, it is preferable for the distillationto be carried out in such a way that the superficial F factor within thedistillation column 11 is at least 0.5 m/s(kg/m³)^(½) and no greaterthan 2.0 m/s(kg/m³)^(½), and preferably at least 0.8 m/s(kg/m³)^(½), andno greater than 1.8 m/s(kg/m³)^(½).

When the superficial F factor is less than 0.5 m/s(kg/m³)^(½), the masstransfer between the liquid and vapor decreases, and the efficiency ofvapor-liquid contact (i.e., distillation efficiency) is reduced. Inaddition, a superficial F factor exceeding 2.0 m/s(kg/m³)^(½) isundesirable due to the tendency for flooding.

In addition, the pressure within the column is preferably in the rangeof 0.5 bar to 5 bar, and more preferably 1.1 bar to 2.5 bar.

When the pressure is less than 0.5 bar, the distillation operationbecomes a low pressure distillation (vacuum distillation) andconsideration must be given to apparatus for pump leaks and the like. Inaddition, if the pressure exceeds 5 bar, since the relative volatilityof the three above-mentioned components becomes even closer to one andseparation becomes more difficult, the disadvantage arises that therequired packing height within the distillation column is increased.

As described above, in the method for enrichment of the heavy oxygenisotopes of the present invention, enrichment of ¹⁶O¹⁷O and ¹⁶O¹⁸O iscarried out by means of cryogenic distillation of an oxygen startingmaterial using a distillation column packed with structured packing, andthereby the effects shown below are obtained.

(1) In contrast to water distillation and NO distillation, since oxygenwhich does not contain other elements is used as the starting material,it is possible to obtain an enriched product with a high concentrationof heavy oxygen isotopes, which does not contain compounds of heavyisotopes of other elements with ¹⁶O.

(2) Since the latent heat of vaporization of oxygen (the startingmaterial) is low (the latent heat of vaporization of oxygen isapproximately ⅙ of that of water), it is possible to reduce the size ofthe heat exchangers (condenser 12 and reboiler 13) compared with thosefor water distillation methods, and thus it is possible to reduce theenergy consumption of the apparatus. For this reason, it is possible toreduce operation costs. In addition, it is possible to miniaturize theheat exchangers and to reduce apparatus costs.

(3) The oxygen starting material. is not a corrosive or toxic gas, andhence is advantageous with regard to ease of handling and safety whencompared with NO-distillation methods in which NO, which is a corrosiveand toxic gas, is used as the starting material.

(4) By means of the use of a distillation column 11 in which structuredpacking 14 and 15 are used, it is possible to reduce liquid hold-up whencompared with situations in which unstructured packing is used, and thusit is possible to shorten the time required to start up the apparatus.Furthermore, it is possible to reduce power costs and the like requiredduring the start-up and thereby to reduce operating costs.

(5) By means of using structured packing, it is possible to increase theefficiency of vapor-liquid contact within the distillation column 11,and thereby increase the efficiency of the heavy isotope enrichment.

(6) In general, since the separation coefficient of oxygen isotopes isextremely close to 1, when a plate distillation column is used as thedistillation column, theoretically several thousand plates are necessaryand the pressure loss is great. In addition, when using unstructuredpacking as well, the pressure loss is great.

In contrast to this, in the method of the above-mentioned embodiment, bymeans of using a distillation column 11 in which structure packing 14and 15, for which the pressure loss is low, are used, it is possible forthe pressure within the column to be set at a lower level. By means ofreducing the pressure within the column, it is possible to increase therelative volatility of ¹⁶O¹⁷O with respect to ¹⁶O¹⁶O, and to increasethe relative volatility of ¹⁶O¹⁸O with respect to ¹⁶O¹⁶O. Thereby, it ispossible to increase the efficiency of the enrichment of ¹⁶O¹⁷O and¹⁶O¹⁸O.

(7) By means of using, as the structured packing 14 and 15,promoting-fluid-dispersion type structured packing with which thevapor-liquid contact occurs while mixing of the liquid and/or the vaporin a direction at right angles to the main flow direction within thedistillation column 11 is promoted, it is possible to increase theefficiency of vapor-liquid contact and to further improve the efficiencyof the enrichment of the heavy oxygen isotopes.

(8) By means of the provision of a condenser 12 and a reboiler 13 in thedistillation column 11, and by using and circulating a medium for heatexchange, such as nitrogen, between the condenser 12 and the reboiler13, it is possible to make use of the coolness of the medium for heatexchange without waste, to suppress energy loss to a minimum and therebyto reduce operating costs.

In addition, since a cryogenic and highly pure oxygen product obtainedfrom a high purity oxygen production apparatus using cryogenicdistillation is used as the oxygen starting material, it is possible touse this oxygen starting material as a cooling source and thereby toreduce operating cost of the apparatus.

In addition, by means of using highly pure oxygen with a purity of99.999% or greater as the oxygen starting material, it is possible toprevent the final product from being contaminated with impurities suchas argon, hydrocarbons such as methane, krypton, xenon,perfluorocarbons, and the like.

In particular, it is possible to prevent high concentrations ofhydrocarbons such as methane, and thereby to prevent the occurrence ofaccidents such as fires.

In the following, the results of a computer simulation for a process ofenrichment of heavy oxygen isotopes by means of vapor-liquid contact anddistillation which occur within the distillation column 11 using theabove mentioned process will be explained.

The distillation theory employed in designing the distillation columnaccording to the present invention and the distillation theory employedin this simulation use a rate model relating to mass transfer, in whichthe so-called H.E.T.P. (Height Equivalent to a Theoretical Plate) orequilibrium stage model were not used.

In the distillation theory using this rate model, the mass flux N isexpressed in the following way using the diffusion flux J and convectionρV.

N=J _(GS)+ρ_(GS)ν_(GS)ω_(GS)

In addition, as the formula for the correlation related to masstransfer, it is possible to give the following.

Sh _(GS)(J _(GS) /N)=A ₁ Re _(G) ^(A2) ·Sc _(GS) ^(A3)

wherein Sh, Re, and Sc are respectively defined by the followingformulae.

Sh _(GS) =Nd/(ρ_(GS) D _(GS)Δω_(GS))

Re _(G)=ρ_(G) U _(G) d/μ _(G)

Sc _(GS)=μ_(GS)/(ρ_(GS) D _(Gs))

N: mass flux [kg/(m²·s)]

J: diffusion flux [kg/(m²·s)]

d: equivalent diameter [m]

D: diffusion coefficient [m²/s]

ρ: density [kg/m³]

ν: velocity [m/s]

ω: concentration [kg/kg]

Sh: Sherwood number [−]

Re: Reynolds number [−]

Sc: Schmidt number [−]

A1, A2, A3: constants determined depending on the system

subscript G: vapor phase

subscript S: vapor-liquid interface

The advantages with this rate model are that it is possible to correctlypredict the mass transfer of an intermediate component within amulti-component system, and it does not give unrealistic results such asthe negative values obtained with H.E.T.P. or Murphree's plateefficiency which occur when making calculations by means of theequilibrium stage model.

The aforementioned model is disclosed in detail in J. A. Wesselingh:“Non-equilibrium modeling of distillation” IChemE Distillation andAbsorption '97, vol. 1, pp. 1-21 (1997).

In the following, as an example of a situation in which the enrichmentapparatus shown in FIG. 1 is used, the results of a simulation of aprocess of enrichment of the heavy oxygen isotopes using theabove-mentioned formula will be explained.

Naturally abundant oxygen contains three types of isotopes (¹⁶O, ¹⁷O and¹⁸O), and the relative abundance of ¹⁶O is 99.759%, the relativeabundance of ¹⁷O is 0.037%, and the relative abundance of ¹⁸O is 0.204%.

Consequently, there are six types of oxygen molecules, ¹⁶O¹⁶O, ¹⁶O¹⁷O,¹⁶O¹⁸O, ¹⁷O¹⁷O, ¹⁷O¹⁸O, and ¹⁸O¹⁸O. However, since the relativeabundances of ¹⁷O and ¹⁸O are small, as shown in Table 3, the relativeabundances of the molecules of ¹⁷O¹⁷O, ¹⁷O¹⁸O, and ¹⁸O¹⁸O are extremelysmall.

TABLE 3 Mass Number Oxygen Molecule Relative Abundance 32 ¹⁶O¹⁶O 0.9951933 ¹⁶O¹⁷O 0.00074 34 ¹⁶O¹⁸O 0.00407 34 ¹⁷O¹⁷O 1.37 × 10⁻⁷ 35 ¹⁷O¹⁸O 1.51× 10⁻⁶ 36 ¹⁸O¹⁸O 4.16 × 10⁻⁶

For this reason, in this simulation, the presence of ¹⁷O¹⁷O, ¹⁷O¹⁸O, and¹⁸O¹⁸O whose relative abundance is small is ignored, and the oxygenstarting material is taken to comprise three types of components(¹⁶O¹⁶O, ¹⁶O¹⁷O, and ¹⁶O¹⁸O).

Table 4 shows the results of a study in which other data was varied fora situation in which the specific surface area of the packing was fixed(500 m²/m³), the concentration of the oxygen isotopes in the productwere at generally fixed levels, and the operating pressure was varied.

Table 5 shows a comparison for variation of other data for a situationin which the column diameter and the packing height (total height of thecolumn) were fixed, and the specific surface area of the packing wasvaried.

TABLE 4 Case 1 Case 2 Case 3 Case 4 Case 5 Specific surface area of the500 500 500 500 500 packing (m²/m³) Internal diameter of thedistillation column (m) 1.970 1.780 1.635 1.555 1.525 Packing height attop of column (m) 62 70 80 75 82 Packing height at bottom of column (m)194 231 280 327 363 Total height of column (m) 256 301 360 402 445 Heatexchange amount of 1900 1900 1900 1900 1900 reboiler/condenser (kW)Pressure (bar) 0.6-1.0 1.1-1.7 2.0-2.9 3.0-4.2 4.0-5.6 Superficial FFactor 1.4-1.7 1.4-1.6 1.3-1.5 1.3-1.4 1.2-1.3 (m/s (kg/m³)^(1/2) Feed101 Pressure (bar) 0.7 1.2 2.2 3.2 4.2 Flow rate (mol/s) 1.00 1.00 1.001.00 1.00 Concentration of 7.38 × 10⁻⁴ 7.38 × 10⁻⁴ 7.38 × 10⁻⁴ 7.38 ×10⁻⁴ 7.38 × 10⁻⁴ ¹⁶O¹⁷O (-) Concentration of 4.07 × 10⁻³ 4.07 × 10⁻³4.07 × 10⁻³ 4.07 × 10⁻³ 4.07 × 10⁻³ ¹⁶O¹⁸O (-) Product vapor 102Pressure (bar) 1.0 1.7 2.9 4.2 5.6 Flow rate (mol/s) 0.0148 0.01480.0148 0.0148 0.0148 Concentration of 8.62 × 10⁻³ 8.61 × 10⁻³ 8.63 ×10⁻³ 8.59 × 10⁻³ 8.60 × 10⁻³ ¹⁶O¹⁷O (-) Concentration of 0.199 0.1940.188 0.179 0.176 ¹⁶O¹⁸O (-) Reboiler vapor 103 Pressure (bar) 1.0 1.72.9 4.2 5.6 Flow rate (mol/s) 278 286 296 305 313 Concentration of 8.62× 10⁻³ 8.61 × 10⁻³ 8.63 × 10⁻³ 8.59 × 10⁻³ 8.60 × 10⁻³ ¹⁶O¹⁷O (-)Concentration of 0.199 0.194 0.188 0.179 0.176 ¹⁶O¹⁸O (-) Reflux liquid104 Pressure (bar) 0.6 1.1 2.0 3.0 4.0 Flow rate (mol/s) 273 280 288 296303 Concentration of 6.20 × 10⁻⁴ 6.20 × 10⁻⁴ 6.20 × 10⁻⁴ 6.21 × 10⁻⁴6.20 × 10⁻⁴ ¹⁶O¹⁷O (-) Concentration of 1.15 × 10⁻³ 1.22 × 10⁻³ 1.30 ×10⁻³ 1.45 × 10⁻³ 1.50 × 10⁻³ ¹⁶O¹⁸O (-) Exhaust vapor 105 Pressure (bar)0.6 1.1 2.0 3.0 4.0 Flow rate (mol/s) 0.985 0.985 0.985 0.985 0.985Concentration of 6.20 × 10⁻⁴ 6.20 × 10⁻⁴ 6.20 × 10⁻⁴ 6.21 × 10⁻⁴ 6.20 ×10⁻⁴ ¹⁶O¹⁷O (-) Concentration of 1.15 × 10⁻³ 1.22 × 10⁻³ 1.30 × 10⁻³1.45 × 10⁻³ 1.50 × 10⁻³ ¹⁶O¹⁸O (-) (The total height of the column doesnot include the height of the liquid collector or the liquiddistributor.)

TABLE 5 Case 2 Case 6 Case 7 Specific surface area of the 500 750 900packing (m²/m³) Internal diameter of the 1.780 1.780 1.780 distillationcolumn (m) Packing height at top 70 60 55 of column (m) Packing heightat bottom 231 241 246 of column (m) Total height of column (m) 301 301301 Heat exchange amount of 1900 1515 1045 reboiler/condenser (kW)Pressure (bar) 1.1-1.7 1.1-1.7 1.1-1.5 Superficial F Factor 1.4-1.61.1-1.3 0.8-0.9 (m/s (kg/m³)^(1/2) Feed 101 Pressure (bar) 1.2 1.2 1.2Flow rate (mol/s) 1.00 1.00 1.00 Concentration of 7.38 × 10⁻⁴ 7.38 ×10⁻⁴ 7.38 × 10⁻⁴ ¹⁶O¹⁷O (-) Concentration of 4.07 × 10⁻³ 4.07 × 10⁻³4.07 × 10⁻³ ¹⁶O¹⁸O (-) Product vapor 102 Pressure (bar) 1.7 1.7 1.5 Flowrate (mol/s) 0.0148 0.0148 0.0148 Concentration of 8.61 × 10⁻³ 1.13 ×10⁻² 1.09 × 10⁻² ¹⁶O¹⁷O (-) Concentration of 0.194 0.201 0.174 ¹⁶O¹⁸O(-) Reboiler vapor 103 Pressure (bar) 1.7 1.7 1.5 Flow rate (mol/s) 286228 156 Concentration of 8.61 × 10⁻³ 1.13 × 10⁻² 1.09 × 10⁻² ¹⁶O¹⁷O (-)Concentration of 0.194 0.201 0.174 ¹⁶O¹⁸O (-) Reflux liquid 104 Pressure(bar) 1.1 1.1 1.1 Flow rate (mol/s) 280 223 154 Concentration of 6.20 ×10⁻⁴ 5.80 × 10⁻⁴ 5.86 × 10⁻⁴ ¹⁶O¹⁷O (-) Concentration of 1.22 × 10⁻³1.12 × 10⁻³ 1.52 × 10⁻³ ¹⁶O¹⁸O (-) Exhaust vapor 105 Pressure (bar) 1.11.1 1.1 Flow rate (mol/s) 0.985 0.985 0.985 Concentration of 6.20 × 10⁻⁴5.80 × 10⁻⁴ 5.86 × 10⁻⁴ ¹⁶O¹⁷O (-) Concentration of 1.22 × 10⁻³ 1.12 ×10⁻³ 1.52 × 10⁻³ ¹⁶O¹⁸O (-) (The total height of the column does notinclude the height of the liquid collector or the liquid distributor.)

FIG. 7 shows the relationship between the pressure within the column,the column diameter, and the height of the packing within the column forCases 1 to 5 obtained by means of the above-mentioned simulation.

From FIG. 7, it can be understood that when the specific surface area ofthe packing is a fixed condition, it is possible to reduce the volume ofthe column by means of increasing the pressure within the column.

However, when the enrichment rate of ¹⁶O¹⁷O is generally fixed, there isa tendency for the pressure to be increased and for the height of thepacking to be increased, and above 3 to 4 bars, the effect of reducingthe volume of the column is reduced.

In addition, from Table 5, in a comparison of situations in which thespecific surface area of the packing is 500, 750, and 900 m²/m³, it isclear that from the point of view of the enrichment efficiency that aspecific surface area for the packing of 750 m²/m³ is advantageous.

On the other hand, by means-of reducing the pressure within thedistillation column, while the diameter of the column is increased, atthe same time, the relative volatility of ¹⁶O¹⁷O with respect to ¹⁶O¹⁶O,and the relative volatility of ¹⁶O¹⁸O with respect to ¹⁶O¹⁶O increasesand thereby it is possible to increase enrichment efficiency for ¹⁶O¹⁷O,and ¹⁶O¹⁸O.

FIG. 8 shows the concentration distribution for the threeabove-mentioned components (¹⁶O¹⁶O, ¹⁶O¹⁷O, and ¹⁶O¹⁸O) within thedistillation column 11 obtained by means of the above-mentionedsimulation.

From this figure, among these components, the concentration of ¹⁶O¹⁸Ogradually increases from the top of the distillation column 11 to thebottom of the distillation column 11.

In contrast to this, among these components, from the top to the bottomof the distillation column 11, the concentration of ¹⁶O¹⁷O increasesonce to a peak and thereafter it decreases gradually as it approachesthe bottom of the distillation column 11.

In this way, when attempting to carryout enrichment of ¹⁶O¹⁷O using onedistillation column, it is clear that there is a fixed limit to thepossible enrichment concentration of ¹⁶O¹⁷O.

For this reason, it is considered that for increasing the concentrationof ¹⁶O¹⁷O to 10% or greater, for example, a method in which a pluralityof distillation columns are used, in which enrichment of ¹⁶O¹⁷O iscarried out in the first distillation column, and the obtained enrichedmaterial is further enriched in the second and subsequent distillationcolumns, is effective.

FIG. 9 shows a suitable enrichment apparatus for enriching ¹⁶O¹⁷O and¹⁶O¹⁸O, and in particular ¹⁶O¹⁷O, to high concentrations. The enrichmentapparatus shown here is equipped with 3 distillation columns (A1˜A3).

The bottom of the first column Al and the center section (anintermediate position between the top of the column and the bottom ofthe column) of the second column A2 are connected by conduit pipes 56 aand 57 a, and the bottom of the second column A2 and the center sectionof the third column A3 are connected by conduit pipes 56 b and 57 b. Inaddition, a conduit pipe 56 c is connected to the bottom of the thirdcolumn A3, and column bottom liquid from the third column A3 can bedrawn out of the system via conduit pipes 56 c and 57 c.

In addition, the conduit pipe 58 which is connected to the centersection of the first column Al is a feed section for introducing oxygenstarting material into the first column A1.

In addition, conduit pipes 59 a and 59 b are for the purpose ofreturning vapor output from the top of the second column A2 to the firstcolumn A1. The conduit pipe 59 b is connected to a position locatedbetween the connection position of the conduit pipe 58, which is theabove-mentioned feed section, and the bottom of the column.

A blower 59 c is provided in the conduit pipe 59, such that the outputvapor from the second column A2 can be pressurized and sent to the firstcolumn A1.

Condensers 60 a, 60 b and 60 c are provided in the vicinities of thetops of the first to third columns A1 to A3 respectively, and reboilers61 a, 61 b, and 61 c are provided in the vicinities of the bottoms ofthe first to third columns A1 to A3 respectively.

When using the above-mentioned enrichment apparatus, firstly oxygenstarting material vapor (111) is introduced into the first column A1 viaconduit pipe 58, which is the feed section, distillation is conductedwithin the first column A1, the column bottom liquid in which theconcentration of heavy isotopes has been increased is vaporized at thereboiler 61 a and a part thereof is introduced into the center sectionof the second column A2 via conduit pipe 57 a.

This column bottom liquid can be extracted from conduit pipe 56 a′ or 56a″ as a product.

The vapor introduced into the second column A2 is distilled within thesecond column A2, the column bottom liquid in which the concentration ofheavy isotopes has been further increased is passed through reboiler 61b and conduit pipe 57 b and introduced into the third column A3, whereadditional distillation is carried out, and thereby a column bottomliquid in which the concentration of heavy isotopes is even furtherincreased is obtained.

This column bottom liquid can be extracted from conduit pipe 56 b′ or 56b″ as a product.

In this situation, it is preferable to suitably set the variousconditions such as the internal column pressure, the column height, thecolumn diameter, and the type of packing, in such as way that within thesecond column A2 (which is the distillation column before final stagedistillation column A3), a concentration peak of ¹⁶O¹⁷O is formed in thecenter section of column, and a mixture of oxygen isotopes comprising¹⁶O¹⁷O at a concentration of 1% or greater, ¹⁶O¹⁸O at a concentration of90% or greater, with main part of the remainder being ¹⁶O¹⁶O, isseparated at the bottom of the distillation column.

In addition, in this case, vapor in the vicinity of the top of thesecond column A2 passes through conduit pipes 59 a and 59 b, and ispressurized using blower 59 c, thereafter, and the recovery rate can beincreased by introducing it into the first column A1. In other words, itis possible to improve the efficiency of the isotope enrichment withinthe first column A1.

Next, the column bottom liquid of the third column A3 passes through thereboiler 61 c and the conduit pipe 57 c and is output from the system asproduct vapor (120). In the above-mentioned distillation process, theconcentration of ¹⁶O¹⁸O within the product vapor (120) can be increasedto 90% or greater by means of suitably setting the above-mentionedvarious conditions.

The vapor from the top of the third column A3 is passed through theconduit pipe 57 d and is output from the system as finished productvapor (118). In the above-mentioned distillation process, theconcentration of ¹⁶O¹⁷O within the finished product vapor (118) can beincreased to 10% or greater by means of suitably setting theabove-mentioned various conditions.

In the Figures, the reference numerals 111˜120 respectively indicate theoxygen starting material vapor (111) which is introduced into the firstcolumn A1 via conduit pipe 58; the vapor (112) output from the top ofthe first column A1; the condensed liquid (113) which is formed byliquefying the vapor output from the top of the first column A1 by meansof condenser 60 a; the vapor (114) which is introduced into the secondcolumn A2 after passing through the reboiler 61 a and the conduit pipe57 a; vapor (115) which is output from the top of the second column A2,passes through conduit pipe 59 b, and is returned to the first columnA1; the liquid (116) which is output from the second column A2,liquefied in the condenser 60 b, and then returned to the second columnA2 again; the vapor (117) which passes through the reboiler 61 b, andthe conduit pipe 57 b, and is introduced into the third column A3; thevapor (118) which is output from the top of the third column A3; theliquid (119) which is drawn of from the top of the third column A3liquefied in the condenser 60 c and then returned again to the thirdcolumn A3; and the vapor (120) which is output from the third column A3through the reboiler 61 c and the conduit pipe 57 c.

In this way, by means of constructing the distillation column from threedistillation columns, i.e. the first to third columns A1 to A3, it ispossible to further enrich the oxygen isotopes enriched in the firstcolumn A1 in the second column A2 and the third column A3.

Consequently, when compared to a situation in which one distillationcolumn is used, it is possible to obtain an enriched product having ahigher isotope enrichment rate, and more specifically, an enrichedproduct (finished product vapor 118) having a concentration of ¹⁶O¹⁷Oof, for example, 10% or greater; and an enriched product (finishedproduct vapor 120) having a concentration of ¹⁶O¹⁸O of, for example, 90%or greater.

In addition, when ¹⁶O¹⁸O is extracted as the finished product, it ispossible to extract the finished product from the bottom of the firstcolumn A1 and the second column A2.

In addition, since the relative volatility of ¹⁶O¹⁷O with respect to¹⁶O¹⁶O is smaller than the relative volatility of ¹⁶O¹⁸O with respect to¹⁶O¹⁶O, enrichment of ¹⁶O¹⁷O is more difficult than enrichment of¹⁶O¹⁸O, but it is possible to sufficiently increase the enrichment ratefor ¹⁶O¹⁷O by means of conducting a multi-stage distillation using firstto third columns A1 to A3.

In addition, in the above-mentioned apparatus, there are threedistillation columns. However, the present invention is not limited tothis. It is possible to have a plurality (n) of distillation columns(A₁˜A_(n)), wherein the bottom portion of the column A_(k) (k: a naturalnumber of (n−1) or less) is connected to the center section of thecolumn A_(k+1) by means of a conduit pipe which directs the columnbottom liquid of column Ak into the column Ak+1. The number ofdistillation columns may be, for example, from 2 to 100.

In addition, under the conditions shown in Table 4 and Table 5, thepacking height of a single distillation column is considerably high atseveral hundred meters, therefore, when actually designing theapparatus, the apparatus can be made compact by dividing thedistillation column into a plurality of columns having a packing heightof from several tens to one hundred meters, and then connecting thesecolumns in a series.

FIG. 10 shows an example of the enrichment apparatus in a situation inwhich the above-mentioned distillation column has been divided.

The apparatus shown in FIG. 10 comprises four distillation columns(i.e., the first column B₁˜fourth column B₄), wherein the bottom portionof the column B_(k) (k: a natural number of 3 or less) is connected inseries to the top of the column B_(k+1) by means of the conduit pipes 63a˜63 c, via liquid feeding means 62 a˜62 c such as a feeding pump forfeeding the liquid output from the column B_(k) to the column B_(k+1);and the lower portion of B_(k) is connected to the top of the columnB_(k+1) by means of the conduit pipes 64 a˜64 c for directing the vaporoutput from the column B_(k+1) to the column B_(k). In addition, acondenser 65 is provided in the vicinity of the top of the first columnB₁, and a reboiler 66 is provided in the vicinity of the-bottom of thefourth column B₄.

In addition, the circulation system indicated by number 69 is designedso as to circulate a medium for heat exchange (for example, nitrogengas) output from the storage tank 71 for the medium for heat exchangethrough a reboiler 66, a condenser 65, a first conduit 73 a of a heatexchanger 73, a blower 72 (a circulatory means), and a second conduit 73b of the heat exchanger 73.

The above-mentioned first conduit 73 a corresponds to the system on theinlet side of the blower 72, and the second conduit 73 b corresponds tothe system on the outlet side of the blower 72.

As the blower 72, it is possible to use a normal temperature compressoror a low-temperature compressor. When using a low-temperature compressoras the blower 72, the heat exchanger. 73 is not necessary.

When using the aforementioned apparatus, a starting material vapor isintroduced via the feed section, conduit pipes 67 and 64 a, into thefirst column B₁ where distillation takes place. Subsequently, a portionof the vapor separated at the top of the column is extracted while theremaining portion is liquefied in the condenser 65, and returned to thefirst column B₁. In addition, the column bottom liquid is introducedinto the second column B₂ via the conduit pipe 63 a.

Subsequently, the column head vapor obtained from the top of the secondcolumn B₂ is returned to the first column B₁ via the conduit pipe 64 a,while the column bottom liquid in the second column B₂ is introducedinto the third column B₃ via the conduit pipe 63 b.

Subsequently, the column head vapor obtained in the third column B₃ isthen returned to the second column B₂ via the conduit pipe 64 b, whilethe column bottom liquid in the third column B₃ is introduced into thefourth column B₄ via the conduit pipe 63 c.

Subsequently, the column head vapor obtained in the fourth column B₄ isreturned to the third column B₃ via the conduit pipe 64 c, while thecolumn bottom liquid in the fourth column A₄ passes through the conduitpipe 63 d, is vaporized by passing through the reboiler 66, and thenoutput from the system through conduit pipe 68.

In the aforementioned apparatus, the conduit pipe 67, which is thefeeding member of the starting material vapor, is connected to anotherconduit pipe 64 a. However, the present invention is not limited tothis, and the conduit pipe which is the feeding member may be connectedto conduit pipes 64 b or 64 c depending on conditions such as theconcentration of isotopes in the starting material vapor, and the like.Alternatively, it could be connected to the center section of eachcolumn.

In addition, it is possible to operate the aforementioned apparatus withthe pressure in each column reduced, by means of inserting a blower intothe extraction path 70 for column head vapor of the first column B₁, oralternatively in conduit pipes 64 a, 64 b, and 64 c for returning thevapor. In addition, a reduced pressure operation (vacuum operation) isalso possible.

Thereby, the relative volatility of each component can be increased,leading to an improved yield. In addition, the efficiency of isotopeseparation is increased, and thus it is possible to decrease the columnheight.

By means of using a plurality of distillation columns as described inthe aforementioned, it is possible to decrease the column height and toconstruct an overall compact apparatus, which in turn makes a reductionin equipment costs possible.

The apparatus shown in FIG. 10 comprises four distillation columns.However, the present invention is not limited to this. A plurality (n)of distillation columns (B_(l)˜B_(n)) may be provided, wherein thebottom of the column B_(k) (k: a natural number of n−1 or less) may beconnected to the top of the column B_(k+1) by means of a conduit pipevia a means for feeding the liquid output from the column B_(k) to thecolumn B_(k+1); and the lower part of the column B_(k) may be connectedto the top of the column B_(k+1) by means of a conduit pipe fordirecting the vapor output from the column B_(k+1) the column B_(k). Thenumber of distillation columns may be, for example, from 2 to 100.

Additionally, in the above case, a condenser is provided at the top ofthe column B₁, and a reboiler is provided at the bottom portion of thecolumn B_(k).

In addition, in the enrichment apparatus shown in the above-mentionedFIG. 1, a normal temperature is shown as an example of the blower 16,and a heat exchanger 17 is provided, however, as shown in FIG. 11, it ispossible for a low-temperature compressor to be used as the blowerindicated by the number 86, and in that situation, a heat exchanger 17is not necessary.

In the enrichment apparatus shown in FIG. 11, the circulation system 81has a conduit pipe 82 for introducing a medium for heat exchange, suchas liquid nitrogen, from the storage tank 18 into a second conduit 12 bof the condenser 12, and a conduit 83 for introducing the vapor orliquid within the second conduit 12 b via the blower 86 into the secondconduit 13 b of the reboiler 13, and a conduit pipe 85 for introducingthe liquid or vapor within the second conduit 13 b via a valve 84 intothe conduit pipe 82.

In this apparatus, the medium for heat exchange which circulates withinthe circulation system 81 is cooled by means of the blower 86, which isa low-temperature compressor, therefore, a heat exchanger 17 is notnecessary.

In addition, FIG. 12 shows an apparatus having a coil type reboiler 91,through which the medium for heat exchange passes, provided in theinterior of the bottom of the distillation column 11, and this is inplace of the reboiler 13 which is provided outside of the distillationcolumn 11 in the enrichment apparatus shown in FIG. 1.

The coil reboiler 91 is such that the column bottom liquid of thedistillation column 11 can be heated by means of heat exchange with themedium for heat exchange, such that a part thereof is vaporized.

In the enrichment apparatus shown in this figure as well, thecirculation system 92 is able to circulate the medium for heat exchangebetween the coil type reboiler 91 and the second conduit 12 b of thecondenser 12, and this is the same as for the apparatus shown in FIG. 1.

Embodiment 1

A computer simulation was conducted for enrichment of heavy oxygenisotopes using the enrichment apparatus shown in FIG. 9. A situation inwhich plate fin type heat exchangers were used as the condensers 60 a,60 b, and 60 c and reboilers 61 a, 61 b and 61 c was assumed.

The data for each of the columns is shown in Table 6. In addition, thedata for each of the condensers and reboilers of each column are shownin Table 7.

In addition, the concentration, pressure, and flow rate for each of thecomponents of the liquids or vapors represented by numbers 111 to 120are shown in Table 8.

In addition, FIGS. 13 to 15 show the concentration distribution for eachof the above-mentioned three components (¹⁶O¹⁶O, ¹⁶O¹⁷O, and ¹⁶O¹⁸O)with increasing height within the first through third columns A1 to A3.

TABLE 6 Embodiment 1 First Second Third distillation distillationdistillation column column column Specific surface area of packing 500500 500 (m²/m³) Inner diameter of distillation 3.00 0.50 0.20 column (m)Height of Packing in the 100 200 200 upper part of column (m) Height ofPacking in the 200 400 150 lower part of column (m) Height of packing(m) 300 600 350 Total height of packing (m) 1250 Heat exchange amount of5500 150 23 reboiler/condenser (kW) Superficial F factor 1.7 1.6 1.6[m/s (kg/m³)^(1/2)]

TABLE 7 Embodiment 1 Amount of First medium Second medium heat exchangetemperature Pressure temperature pressure (kW) type (K) (bar) type (K)(bar) First column condenser 5500 oxygen 91.0 1.10 nitrogen 86.0 2.51Second column condenser 150 oxygen 91.0 1.10 nitrogen 86.0 2.51 Thirdcolumn condenser 23 oxygen 91.0 1.10 nitrogen 86.0 2.51 First columnreboiler 5500 oxygen 95.7 1.73 nitrogen 101.2 8.46 Second columnreboiler 150 oxygen 99.2 2.38 nitrogen 104.2 10.30 Third column reboiler23 oxygen 96.2 1.83 nitrogen 101.2 8.46

TABLE 8 Pres- Concentration sure Flow Rate No ¹⁶O¹⁶O (-) ¹⁶O¹⁷O (-)¹⁶O¹⁸O (-) (bar) (mol/s) 111 9.95 × 10⁻¹ 7.38 × 10⁻⁴ 4.07 × 10⁻³ 1.322.86 112 9.98 × 10⁻¹ 6.71 × 10⁻⁴ 1.29 × 10⁻³ 1.10 2.85 113 9.98 × 10⁻¹6.71 × 10⁻⁴ 1.29 × 10⁻³ 1.10 8.09 × 10⁻² 114 8.01 × 10⁻¹ 7.99 × 10⁻³1.91 × 10⁻¹ 1.51 4.22 × 10⁻² 115 9.92 × 10⁻¹ 4.14 × 10⁻³ 3.48 × 10⁻³1.10 3.38 × 10⁻² 116 9.92 × 10⁻¹ 4.14 × 10⁻³ 3.48 × 10⁻³ 1.10 2.22 × 10117 3.48 × 10⁻² 2.34 × 10⁻² 9.42 × 10⁻¹ 1.52 8.44 × 10⁻³ 118 3.24 × 10⁻¹1.21 × 10⁻¹ 5.56 × 10⁻¹ 1.10 8.44 × 10⁻⁴ 119 3.24 × 10⁻¹ 1.21 × 10⁻¹5.56 × 10⁻¹ 1.10 3.38 120 2.69 × 10⁻³ 1.26 × 10⁻² 9.85 × 10⁻¹ 1.83 7.60× 10⁻³

As shown in FIG. 13 through FIG. 15, in the above-mentioned simulation,the obtained results are a concentration of ¹⁶O¹⁸O of 19.1% and aconcentration of the ¹⁶O¹⁷O of 0.799% in the column bottom liquid of thefirst column A1.

When a part of this column bottom liquid is supplied to the centersection of the second first A1 and distillation conducted, the obtainedresults are a concentration of ¹⁶O¹⁸O of 94.2% and a concentration ofthe ¹⁶O¹⁷O of 2.34% in the column bottom liquid of the second column A2.

Subsequently, when this column bottom liquid is supplied to the centersection of the third column A3 and distillation conducted, the resultsare that a liquid containing ¹⁶O¹⁸O at a high concentration of 98.5% isobtained from the bottom of the third column A3, and a vapor containing¹⁶O¹⁷O at a high concentration of 12.1% is obtained at the top of thethird column A3.

From the results of the above-mentioned simulation, it is clear that bymeans of the above-mentioned apparatus it is possible to produce0.000844 mol/s (a yearly production rate of 0.88 tons) of ¹⁶O¹⁷O at aconcentration of 12.1%, and 0.00760 mol/s (a yearly production rate of8.1 tons) of ¹⁶O¹⁸O at a concentration of 98.5% with respect to a 2.86mol/s feed rate.

As explained above, the method for enrichment of the heavy oxygenisotopes of the present invention is enrichment of ¹⁶O¹⁷O and ¹⁶O¹⁸O bymeans of cryogenic distillation of an oxygen starting material using adistillation column packed with structured packing, and therefore it ispossible to obtain the effects indicated below.

(1) In contrast to water distillation and NO distillation, since oxygenwhich does not contain other elements is used as the starting material,it is possible to obtain an enriched product with a high concentrationof heavy oxygen isotopes, which does not contain compounds of heavyisotopes of other elements with ¹⁶O.

(2) Since the latent heat of vaporization of oxygen (the startingmaterial) is low (the latent heat of vaporization of oxygen isapproximately ⅙ of that of water), it is possible to reduce the size ofdistillation column and the heat exchangers (reboiler, condensers, andthe like) compared with those for water distillation methods, and thusit is possible to reduce operation costs and apparatus costs.

(3) The oxygen starting material is not a corrosive or toxic gas, andhence is advantageous with regard to ease of handling and safety whencompared with NO-distillation methods in which NO, which is a corrosiveand toxic gas, is used as the starting material.

(4) By means of the use of a distillation column in which structuredpacking is used, it is possible to reduce liquid hold-up and to shortenthe time required to start up the apparatus. Furthermore, it is possibleto reduce the operating costs associated therewith.

(5) By means of using structured packing, it is possible to increase theefficiency of vapor-liquid contact within the distillation column, andthereby to increase the efficiency of the heavy isotope enrichment.

(6) By means of the use of structured packing for which the pressureloss is low, it is possible for the pressure within the column to be setat a lower level. For this reason, it is possible to conduct thedistillation under conditions in which the relative volatility of eachof the components is comparatively large, and thereby it is possible toincrease the enrichment efficiency for oxygen molecules (¹⁶O¹⁷O and¹⁶O¹⁸O) which contain heavy isotopes.

(7) By means of using, as the structured packing,promoting-fluid-dispersion type structured packing with which thevapor-liquid contact occurs while mixing of the liquid and/or the vaporin a direction at right angles to the main flow direction within thedistillation column is promoted, it is possible to increase theefficiency of vapor-liquid contact and to further improve the efficiencyof the enrichment of the heavy oxygen isotopes.

(8) By means of the provision of a condenser and a reboiler in thedistillation column, and by using and circulating a medium for heatexchange between the condenser and the reboiler, it is possible to makeuse of the coolness of the medium for heat exchange without waste, tosuppress energy loss to a minimum and thereby to reduce operating costs.

(9) By means of a plurality of distillation columns, it is possible tofurther enrich oxygen isotopes enriched in one column in the othercolumns. Consequently, compared with a situation in which only onedistillation column is used, it is possible to sufficiently increase theenrichment rate of ¹⁶O¹⁷O in particular.

In addition, by means of dividing a single distillation column into aplurality of columns and then connecting them in series, it is possibleto make the apparatus as a whole compact.

FIG. 16 shows another embodiment of the apparatus for enrichment of theheavy oxygen isotopes of the present invention. The apparatus shown herecomprises a first distillation column 201 for enriching an oxygenstarting material in oxygen molecules which contain heavy oxygenisotopes (¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O, ¹⁷O¹⁸O and ¹⁸O¹⁸O) by means ofcryogenic distillation of an oxygen starting material containing heavyoxygen isotopes; an isotope exchanger 203 which is an isotope scramblerfor increasing by means of isotope scrambling the concentration ofoxygen molecules which only contain heavy isotopes (¹⁷O¹⁷O, ¹⁷O¹⁸O and¹⁸O¹⁸O) within the enriched material obtained from the distillationcolumn 201, and a second distillation column 202 for further enrichmentof the oxygen molecules which contain heavy oxygen isotopes by means ofcryogenic distillation of the enriched material in which theconcentration of heavy isotope molecules of oxygen has been increased bymeans of the above-mentioned isotope exchanger 203.

The inside of the first and second distillation columns 201 and 202 arepacked with structured packing 206.

As the structured packing 206, it is possible to suitably use theabove-mentioned non-promoting-fluid-dispersion type structured packingand/or promoting-fluid-dispersion type structured packing.

In addition, in order to make the vapor-liquid contact within thedistillation columns 201 and 202 proceed more efficiently, it isnecessary to provide one or more liquid collectors and liquiddistributors (not shown in the figures) within each distillation column201 and 202.

In FIG. 16, in the vicinity of the tops of the distillation columns 201and 202, condensers 5 and 7 for cooling and liquefying at least a partof the vapor output from the tops of distillation columns 201 and 202respectively are provided, and in the vicinity of the bottom of thedistillation columns 201 and 202, reboilers 6 and 8 for heating andvaporizing at least a part of the liquid output from the bottom of thedistillation columns 201 and 202 are provided.

The condensers 5 and 7 each have a first conduit 5 a and 7 a into whichvapor output from the top of distillation columns 201 and 202 isintroduced, and second conduits 5 b and 7 b through which a medium forheat exchange passes, and are made such that the above-mentioned outputvapor can be cooled and liquefied by means of heat exchange with themedium for heat exchange.

As condensers 5 and 7, it is preferable to use plate fin type heatexchangers or straight pipe type heat exchangers. Since the amount ofthe medium for heat exchange required for distillation is small, it ispreferable for the condensers 5 and 7 to be of a non-submerged typewhich are provided outside of the distillation columns.

The reboilers 6 and 8 each have a first conduit 6 a and 8 a into whichliquid output from the distillation columns 201 and 202 is introduced,and second conduits 6 b and 8 b through which the medium for heatexchange passes, and are made such that the above-mentioned outputliquid can be heated and vaporized by means of heat exchange with themedium for heat exchange.

As the reboilers 6 and 8, it is preferable to use plate fin type heatexchanger.

In addition, the reboilers 6 and 8 may be installed outside or insidethe distillation columns 201 and 202, but for the purpose of easymanufacture, it is preferable for the reboilers 6 and 8 to be installedoutside as in the apparatus shown in the figure. When the reboilers areprovided internally within the distillation columns 201 and 202, it ispossible to use the coil type reboiler described below.

The isotope exchanger 203 has an external container (not shown in thefigure) and within this external container, an isotope exchange catalyst(not shown in the figure). As this isotope exchange catalyst, catalystscontaining at least one type selected from the group comprising tungsten(W), tantalurn (Ta), palladium (Pd), rhodium (Rh), platinum (Pt), andgold (Au) can be used.

The isotope exchanger 203 is made such that the heavy isotope enrichedmaterial obtained by means of the distillation column 201 is introducedinto the reactor and brought into contact with the above-mentionedisotope exchange catalyst, then isotope exchange (described below)within the enriched material is promoted, and thereby it is possible toincrease the concentration of heavy isotope oxygen molecules within theenriched material.

In addition, as the isotope exchange catalysts, in addition to thosementioned above, it is possible to use a catalyst including at least onetype selected from the group comprising Ti-oxide, Zr-oxide, Cr-oxide,Mn-oxide, Fe-oxide, Co-oxide, Ni-oxide, Cu-oxide, Al-oxide, Si-oxide,Sn-oxide, and V-oxide.

The second conduit 5 b of the condenser 5 and the second conduit 6 b ofthe reboiler 8 are connected by means of a circulation system (omittedfrom the figure) the same as the circulation system 19 shown in FIG. 1.By means of the circulation of a medium for heat exchange within thiscirculation system, the liquid or the vapor within the first conduits 5a and 6 a can respectively be vaporized or liquefied.

In the same way, the second conduit 7 b of the condenser 7 and thesecond conduit 8 b of the reboiler 6 are connected by means of acirculation system (omitted from the figure) the same as the circulationsystem 19 shown in FIG. 1.

In the following, as an example of a situation in which the apparatusshown in FIG. 16 is used, another embodiment of the enrichment method ofthe present invention will be explained in detail.

Firstly, via conduit pipe 220 which is the feed section connected to thefirst distillation column 201, oxygen starting material vapor issupplied to the interior of the distillation column 201 as firstdistillation column feed 211.

The oxygen starting material which is supplied to the interior of thedistillation column 201 rises within the distillation column 201, andpasses over the packing 206, at which time it makes vapor-liquid contactwith the circulating liquid (the descending liquid) described below andis distilled.

The oxygen molecules containing heavy isotopes (¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O,and ¹⁷O¹⁸O) within the oxygen starting material vapor are more likely tocondense due to their high boiling points, and the condensed liquidflows down with the reflux liquid within the distillation column 201 asthe descending liquid.

Accordingly, oxygen vapor (¹⁶O¹⁶O enriched vapor), having a decreasedconcentration of the heavy isotopes, becomes enriched at the top of thedistillation column 201.

The enriched vapor is then output from the distillation column 201 viathe conduit pipe 221, and a portion of the vapor is introduced into thefirst conduit 5 a of the condenser 5, where it is condensed by means ofheat exchange with the medium for heat exchange flowing within thesecond conduit 5 b, and is returned to the top of the distillationcolumn 201 as a reflux liquid.

The remaining portion of the aforementioned enriched vapor output fromthe distillation column 201 via the conduit pipe 221 is discharged outof the system as exhaust vapor 213 via the conduit pipe 222.

The reflux liquid introduced into the top of the first distillationcolumn 201 becomes descending liquid and flows down over the surface ofthe structured packing 206 while making vapor-liquid contact with theoxygen starting material vapor which is ascending within thedistillation column 201, and reaches the bottom of the distillationcolumn 201. In this process of vapor-liquid contact, the descendingliquid becomes enriched with oxygen molecules containing heavy oxygenisotopes (¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O, ¹⁷O¹⁸O, and ¹⁸O¹⁸O) which have agreater tendency to liquefy.

Liquid which accumulates at the bottom of the distillation column 201(hereinafter, referred to as the “column bottom liquid”) is output fromthe distillation column 201 via conduit pipe 223 and is introduced intothe first conduit 6 a of the reboiler 6, where it is vaporized by meansof heat exchange with the medium for heat exchange flowing within thesecond conduit 6 b. Subsequently, it is output from the reboiler 6, anda portion thereof is reintroduced as reboiler vapor into the bottom ofthe distillation column 201 and becomes ascending vapor which riseswithin the distillation column 201.

The remaining portion of the vapor output from the first conduit 6 a ofthe reboiler 6 is introduced via conduit pipe 224 into the isotopeexchanger 203 as first distillation column output vapor 212 which is theenriched material enriched with heavy oxygen isotopes.

In the isotope scrambler (i.e., the isotope exchanger 203) into whichthe first distillation column output vapor 203 is introduced, isotopeexchange is conducted by means of an isotope exchange catalyst packed inthe isotope exchanger 203. Isotope exchange is a reaction whereincoupled atoms in a two-atom molecule are exchanged with other atoms onthe surface of a sufficiently heated catalyst

In other words, if, for example, A, B, C, and D are, respectively, anyone of the isotope atoms, ¹⁶O, ¹⁷O, and ¹⁸O, isotope exchange is areaction in which:

AB+CD=AC+BD; or AB+CD=AD+BC

If a particular isotope atom is considered, after sufficient time haspassed, an isotope atom which couples to form a molecule is randomlydetermined according to the abundance ratio of each isotope constituentprior to isotope exchange.

Accordingly, the abundance ratio of each isotope in the reactantmaterial (i.e., oxygen molecule) obtained by means of isotope exchangein the isotope exchanger 203 is determined according to the abundanceratio of each isotope in the first column output vapor 212.

In the following, this will be explained in more detail.

The components of ¹⁶O¹⁶O, ¹⁶O¹⁷O, and ¹⁶O¹⁸O are present in the outputvapor 212. If the respective molar ratios of these components is Y₁₁,Y₁₂, and Y₁₃, since each of these component oxygen molecules randomlyexchanges coupled oxygen atoms in the isotope scrambler, theconcentration of each component after the isotope scrambling is asfollows:

¹⁶O¹⁶O: (Y₁₁+Y₁₂/2+Y₁₃/2)²  (i)

¹⁶O¹⁷O: (Y₁₁+Y₁₂/2+Y₁₃/2)Y₁₂  (ii)

¹⁶O¹⁸O: (Y₁₁+Y₁₂/2+Y₁₃/2)Y₁₃  (iii)

¹⁷O¹⁷O: Y² ₁₂/4  (iv)

¹⁷O¹⁸O: Y₁₂Y₁₃/2  (v)

¹⁸O¹⁸O: Y² ₁₃/4  (vi)

The sum of these constituent concentrations equals 1.

As described above, the phenomena in which, in the presence of aplurality of molecules which contain isotopes, each molecule randomlyexchanges the coupled atoms from which it is formed is called “isotopescrambling”, and the apparatus in which this takes place is called an“isotope scrambler”. The above-mentioned embodiment is an example inwhich an isotope exchanger which uses a catalyst is employed as anisotope scrambler.

By means of the aforementioned isotope exchange, heavy isotope oxygenmolecules (¹⁸O¹⁸O, ¹⁷O¹⁸O, and ¹⁷O¹⁷O) are formed from ¹⁶O¹⁷O and¹⁶O¹⁸O, and thereby the concentration of heavy isotope oxygen moleculesin the aforementioned first distillation column output vapor 212 isincreased.

The vapor in which the concentration of heavy isotope oxygen moleculeshas been increased in this way is then supplied to the seconddistillation column 202, via the conduit pipe 225, as the seconddistillation column feed 214, and ascends within the distillation column202 as ascending vapor while making vapor-liquid contact with thedescending liquid (i.e., reflux liquid), which flows down over thesurface of the packing 206, and reaches the top of the distillationcolumn 202. On the other hand, the descending liquid eventually reachesthe bottom portion of the distillation column 202.

In this process of vapor-liquid contact, the descending liquid becomesenriched in the heavy isotope oxygen molecules (¹⁸O¹⁸O, ¹⁷O¹⁸O, and¹⁷O¹⁷O) generated by means of the above-mentioned isotope scrambling,and the ascending vapor becomes enriched in the ¹⁶O¹⁶O generated bymeans of the isotope scrambling.

The column bottom liquid of the second distillation column 202 is outputfrom the distillation column 202, via the conduit pipe 226, and isvaporized in the reboiler 8. Subsequently, the resultant vapor isdivided into two portions, one of which is discharged, via the conduitpipe 227, out of the system as output vapor 215 as a finished product.

The remaining portion of the vapor of the column bottom liquid, outputfrom the distillation column 202 and vaporized in the reboiler 8, isreturned again to the lower portion of the distillation column 202 asascending vapor.

The re-boiled vapor introduced into the second distillation column 202ascends in the distillation column 202, and is distilled by means ofvapor-liquid contact with the aforementioned descending liquid whenpassing through the packing 206, in the same manner as theaforementioned feed vapor.

The vapor separated at the head of the column is output from thedistillation column 202 via the conduit pipe 228, and a portion thereofis returned, via the condenser 7, to the top of the distillation column202 as the reflux liquid.

The remaining portion of the aforementioned separated vapor which hasbeen output from the distillation column 202 via the conduit pipe 228,pass through the conduit pipe 229 and blower 229 a, and are returned tothe first distillation column 201 as returned vapor 216.

In this distillation operation in which first and second distillationcolumns 201 and 202 are used, the operating pressure is set in the rangeof 0.5 bar to 5 bar, preferably in the range of 1.1 bar to 2.5 bar, andmore preferably in the range of 1.1 bar to 1.8 bar.

The superficial F factor in the distillation columns 201 and 202 is setto at least 0.5 m/s/kg/m³)^(½) and no greater than 2.0 m/s(kg/m³)^(½),and preferably to at least 0.8 m/s(kg/m³)^(½), and no greater than 1.8m/s(kg/m³)^(½).

If the superficial F factor is less than 0.5 m/s(kg/m³)^(½), masstransfer between the liquid and the vapor declines, leading to adeterioration of the efficiency of vapor-liquid contact (i.e.,distillation efficiency). In addition, a superficial F factor exceeding2.0 m/s(kg/m³)^(½) is undesirable due to a tendency towards flooding.

As the medium for heat exchange which flows within the second conduit 5b of the condenser 5 and the second conduit 6 b of the reboiler 6, it ispossible to use nitrogen, oxygen, air or the exhaust gas of an airseparation unit.

By means of the above-mentioned method, in the same way as for theenrichment method in which the apparatus shown in FIG. 1 is used, it ispossible to obtain the following effects.

(1) Since oxygen which does not contain other elements is used as thestarting material, it is possible to obtain an enriched product with ahigh concentration of heavy oxygen isotopes.

(2) Since the latent heat of vaporization of oxygen (the startingmaterial) is low, it is possible to reduce the size of the distillationcolumns, the heat exchangers, and the like compared with those for waterdistillation methods, and thus it is possible to reduce apparatus costsand operation costs.

(3) Since the oxygen starting material is not a corrosive or toxic gas,it is advantageous with regard to ease of handling and safety.

(4) By means of the use of a distillation column in which structuredpacking is used, it is possible to reduce liquid hold-up, and thus it ispossible to shorten the time required to start up the apparatus.Furthermore, it is possible to reduce operating costs associatedtherewith.

(5) By means of using structured packing, it is possible to increase theefficiency of vapor-liquid contact within the distillation column, andthereby it is possible to increase the efficiency of the isotopeenrichment.

(6) By means of using structured packing, the pressure loss for which islow, it is possible to carry out the distillation under conditions inwhich the relative volatility of each component is comparatively largeand thereby it is possible to increase the efficiency of the enrichmentof oxygen molecules containing heavy isotopes.

(7) By means of using promoting-fluid-dispersion type structured packingas the structured packing, it is possible to increase the efficiency ofvapor-liquid contact, and thereby it is possible to further increase theefficiency of the enrichment of heavy oxygen isotopes.

(8) By means of the provision of a condenser and a reboiler in thedistillation column, and by using and circulating a medium for heatexchange between the condenser and the reboiler, it is possible to makeuse of the coolness of the medium for heat exchange without waste, tosuppress energy loss to a minimum and thereby to reduce operating costs.

(9) By means of the use of a plurality of distillation columns, it ispossible to obtain an enriched product for which the ratio of enrichmentis even higher. In addition, it is possible to reduce the height of thedistillation columns, and to make the construction of the apparatus as awhole compact.

In the method of the present embodiment, in addition to these effects,the following effects are also possible.

(10) After the enrichment of an oxygen starting material in oxygenmolecules containing heavy oxygen isotopes (¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O,¹⁷O¹⁸O, and ¹⁸O¹⁸O) by means of the cryogenic distillation of an oxygenstarting material which contains heavy oxygen isotopes, theconcentration of heavy isotope oxygen molecules (¹⁸O¹⁸O, ¹⁷O¹⁸O, and¹⁷O¹⁷O which are oxygen molecules which comprise only heavy isotopes)within the enriched material is increased by means of isotope exchange,and thereby it is possible to obtain a finished product containing ahigh concentration of heavy oxygen isotopes.

In contrast to this, in a method which uses only an oxygen distillationmethod, since a major portion of the oxygen molecules which containheavy oxygen isotopes for enrichment are ¹⁶O¹⁷O and ¹⁶O¹⁸O, the ratio ofthe atoms of ¹⁷O and ¹⁸O (which are of interest) is limited to less than50%.

(11) By means of the carrying out the isotope scrambling using anisotope exchanger equipped with an isotope exchange catalyst whichpromotes isotope exchange in the above-mentioned enriched material, itis possible to simplify the apparatus structure and to reduce equipmentcosts.

FIG. 17 shows yet another embodiment of the enrichment apparatus forheavy oxygen isotopes of the present invention. The apparatus shown herediffers from the apparatus shown in FIG. 16 in that an isotope exchanger207 is provided in the stage after the second distillation column 202,and a third distillation column 204 is provided in the stage after theisotope exchanger 207.

It is possible for this isotope exchanger 207 to have the same structureas the above-mentioned isotope exchanger 203.

The third distillation column 204 may be packed with structured packing206 in the same way as the first and second distillation columns 201 and202.

The specific surface area of the above-mentioned packing 206 ispreferably in the range of 350 m²/m³ to 1200 m²/m³, and preferably 500m²/m³ to 750 m²/m³. When the specific surface area is less than 350m²/m³, the vapor-liquid contact surface area is small and the efficiencyof the vapor-liquid contact is reduced. A specific surface areaexceeding 1200 m²/m³ is not preferred due to a tendency towardsflooding.

A condenser 9 comprising first and second conduits 9 a and 9 b isprovided in the vicinity of the top of the third distillation column204, and a reboiler 10 comprising first and second conduits 10 a and 10b is provided in the vicinity of the bottom of the third distillationcolumn 204. The second conduit 9 b of the condenser 9 is connected tothe second conduit 10 b of the reboiler 10 via a circulatory system fora medium for heat exchange (not shown in the figures), which isconstructed in the same manner with the aforementioned circulatorysystem 19.

In carrying out enrichment, of the heavy oxygen isotopes using theaforementioned apparatus, firstly, in accordance with the processdescribed above, the first distillation column output vapor 212, havingpassed through the first distillation column 201, is introduced into theisotope exchanger 203, where the concentration of heavy isotope oxygenmolecules in the enriched material is increased by means of isotopeexchange, and then this is introduced into the second distillationcolumn 202, where it is further distilled.

Subsequently, the column bottom liquid of the second distillation column202 is vaporized by means of the reboiler 8, and a portion thereof isreturned to the second distillation column 202, while the remainingportion is introduced into the isotope exchanger 207 via the conduitpipe 230 as output vapor 215.

In the isotope exchanger 207, the output vapor 215 is brought intocontact with the aforementioned isotope exchange catalyst and theconcentration of heavy isotope oxygen molecules (i.e., ¹⁸O¹⁸O, ¹⁸O¹⁷O,and ¹⁷O¹⁷O, and particularly ¹⁸O¹⁸O and ¹⁷O¹⁸O) is increased by means ofthe aforementioned isotope exchange.

The vapor, in which the concentration of oxygen molecules of heavyoxygen isotopes (in particular ¹⁸O¹⁸O and ¹⁷O¹⁸O) has been increased bymeans of the isotope exchanger 207, is supplied via the conduit pipe 231to the third distillation column 204 as the third distillation columnfeed 217, and is distilled by means of vapor-liquid contact in the thirddistillation column 204. In this process of vapor-liquid contact, thedescending liquid is further enriched in heavy oxygen isotopes (and¹⁸O¹⁸O in particular).

The column bottom liquid is introduced from the distillation column 204via the conduit pipe 232 into the reboiler 10, and discharged afterbeing vaporized. A portion thereof is discharged, via the conduit pipe235, out of the system as output vapor 218 for use as a finishedproduct.

The remaining portion of the vapor obtained by means of the vaporizationof the column bottom liquid of the third distillation column 204 in thereboiler 10 is returned to the lower portion of the distillation column204.

The vapor introduced into the third distillation column 204 ascendswithin the distillation column 204, and is distilled by means ofvapor-liquid contact with the aforementioned descending liquid whilepassing through the packing 206.

The vapor separated at the top of the column is discharged from thedistillation column 204 via the conduit pipe 233, and a portion thereofis returned, via the condenser 9, to the top of the distillation column204 as reflux liquid.

The remaining portion of the aforementioned separated vapor isdischarged, via the conduit pipe 234, out of the system as exhaust vapor219. The exhaust vapor 219 may also be returned to the distillationcolumn 202 (shown with a broken line in FIG. 17).

In the distillation operation which utilizes the above-mentioned thirddistillation column 204, the operating pressure is set in the range of0.5 bar to 5 bar, preferably in the range of 1.1 bar to 2.5 bar, andmore preferably in the range of 1.1 bar to 2.0 bar.

The superficial F factor within the distillation column 204 is set to atleast 0.5 m/s(kg/m³)^(½) and no greater than 2.0 m/s(kg/m³)^(½), andpreferably to at least 0.8 m/s(kg/m³)^(½), and no greater than 1.8m/s(kg/m³)^(½).

If the superficial F factor is less than 0.5 m/s(kg/m³)^(½), masstransfer between the liquid and the vapor declines, leading to adeterioration in the efficiency of vapor-liquid contact (i.e.,distillation efficiency). In addition, a superficial F factor exceeding2.0 m/s(kg/m³)^(½) is undesirable due to a: tendency towards flooding.

In the method of the above-mentioned embodiment, it is possible toobtain a product containing a high concentration of heavy oxygenisotopes (in particular, ¹⁸O¹⁸O), by means of increasing theconcentration of the heavy isotope oxygen molecules (i.e., ¹⁸O¹⁸O and¹⁷O¹⁸O) in the output vapor 215, which has passed through the firstdistillation column 201, the isotope exchanger 203, and the seconddistillation column 202, using the isotope exchanger 207; and increasingthe concentration of the heavy oxygen isotopes (¹⁸O¹⁸O in particular) inthe feed 217 through distillation of the obtained enriched material(i.e., the third distillation column feed 217) in the third distillationcolumn 204.

In particular, it is possible to set a low column height since theenriched material fed into the third distillation column 204 is enrichedin ¹⁷O¹⁸O and ¹⁸O¹⁸O, both of which comprise large separation factors.

FIG. 18 shows another embodiment of the apparatus for enrichment of theheavy oxygen isotopes of the present invention. The apparatus shown herediffers from the apparatus shown in FIG. 17 by being equipped with afourth distillation column 205 in the stage after the third distillationcolumn 204.

Each of the distillation columns 201, 202, and 204, and the isotopeexchangers 203 and 207 may be constructed in the same manner as shown inFIG. 17.

A condenser and reboiler (not shown in the figures), similar to the onesshown in FIG. 17 are provided in each of the distillation columns 201,202, 204, and 205. In addition, in FIG. 18, a portion of the conduitpipes have been omitted and are not shown.

The fourth distillation column 205 may be packed with structured packing206, in a similar way as in the first through third distillationcolumns.

In carrying out the enrichment of heavy oxygen isotopes using theaforementioned apparatus, in accordance with the above-describedprocess, enrichment of heavy oxygen isotopes is carried out in the firstdistillation column 201 to produce a first distillation column outputvapor 212, which is then introduced into the isotope exchanger 203 wherethe concentration of heavy isotope oxygen molecules is increased bymeans of isotope exchange. The second distillation feed 214 which haspassed through the isotope exchanger 203 is then introduced into thesecond distillation column 202, and the concentration of the heavyisotope oxygen molecules (¹⁸O¹⁸O and ¹⁷O¹⁸O in particular) in the outputvapor 215 of the second distillation column 202 is increased by means ofthe isotope exchanger 207. The resultant third distillation column feed217 is then supplied to the third distillation column 204.

At this time, it is preferable to create a maximum concentration of¹⁷O¹⁸O in the middle section of the column (i.e., at a position betweenthe top of the column and the bottom of the column) in the thirddistillation column 204; in other words, to create a peak in theconcentration of ¹⁷O¹⁸O at the middle section of the column, by means ofappropriately setting various conditions, such as the inner pressure ofthe column, the reflux ratio, the column height, the column diameter,the type of packing, and the like.

In this manner, the concentration of ¹⁶O¹⁸O at the bottom of the thirddistillation column 204 is suppressed, while the concentration of ¹⁷O¹⁸Ois increased at the bottom portion of the third distillation column 204.Additionally, ¹⁸O¹⁸O can be recovered at a high recovery rate at thebottom of the third distillation column 204.

Accordingly, by means of setting the operating conditions of the thirddistillation column 204, it is possible to enrich ¹⁸O to a highconcentration at the bottom of the third distillation column 204, and inaddition to enrich ¹⁷O to a high concentration at the top of the columnof the third distillation column.

Subsequently, the output vapor 218, in which heavy isotope oxygenmolecules (in particular, ¹⁷O¹⁸O, and ¹⁸O¹⁸O) have been enriched in thebottom of the third distillation column 204, is introduced into thefourth distillation column 205.

In the fourth distillation column 205, enriched liquid in which theconcentration of ¹⁸O¹⁸O in particular has been increased collects at thebottom of the column by means of distillation. The output liquid is thenvaporized in the reboiler (not shown in the figure), and, subsequently,a portion thereof is discharged out of the system as output vapor 209(i.e., finished product vapor). Additionally, the remaining portion isthen introduced into the lower section of the column 205, and forms theascending vapor.

In addition, the separated vapor at the top of the column is dischargedout of the system as output vapor 210.

In the method of the present embodiment, by means of using a fourthdistillation column 205, it is possible to further increase theconcentration of the heavy isotope oxygen molecules (i.e., ¹⁸O¹⁸O and¹⁷O¹⁸O) in the output vapor 218, which has passed sequentially throughthe first distillation column 201, the isotope exchanger 203, the seconddistillation column 202, the isotope exchanger 207, and the thirddistillation column 204.

Accordingly, it is possible to obtain an output vapor 209 in which theconcentration of ¹⁸O¹⁸O is increased, for example, to 99% or greater. Inaddition, it is possible to obtain an output vapor 210 in which theconcentration of ¹⁷O¹⁸O is increased, for example, to 10% or greater.

In addition, it is possible to set a low column height since theenriched material fed into the fourth distillation column 205 isenriched in ¹⁷O¹⁸O and ¹⁸O¹⁸O, both of which comprise large separationfactors.

In addition, the apparatus according to the present invention is notlimited to the above-mentioned constructions, and the aforementioneddistillation columns 201, 202, 204 and 205 may also be divided into aplurality of columns as shown in FIG. 10.

As the isotope scrambler used in the present invention, it is possibleto use the apparatus shown in FIG. 19.

The isotope scrambler 300 shown here conducts isotope exchange by meansof conducting hydrogenation using a catalyst, followed by electrolysisof the obtained produced water, and comprises a catalytic column 302which is a reaction system for producing water by means of reactinghydrogen with output vapor from the distillation column located at thestep in front of the isotope scrambler; a cooler 308 for condensing andrecovering the produced water; water storage tanks 311 a and 311 b forstoring the produced water recovered at the cooler 308; an electrolysisunit 320 for conducting electrolysis of the aforementioned producedwater; an oxygen purifier 327 for oxidizing impurities in the oxygenobtained by means of the electrolysis; and a trap 328 for removing theoxidized impurities.

As the catalytic column 302, it is possible to use columns packed withhydrogen and oxygen reactive catalysts. As these catalysts, it ispreferable to use a catalyst containing at least one type of metalselected from the group comprising Pt, Pd, Rh, Ru, Au, Ni, Cu, and Mn.

In addition, it is possible to use a catalyst, in which theabove-mentioned metals (Pt, Pd, Rh, etc.) are carried by at least oneselected from the group comprising Al-oxide, Si-oxide, Ti-oxide,Zr-oxide, Cr-oxide, V-oxide, Co-oxide, Mn-oxide, or the like.

It is preferable for the catalytic column to be constructed such thatthe reaction between hydrogen and oxygen occurs at a temperature of 150°C. or below. A temperature higher than 150° C. causes an exchangereaction between the oxygen in the aforementioned oxide and oxygen inthe aforementioned enriched material, and is hence undesirable.

Preferred examples of the oxygen purifier 327 include purifiers providedwith catalysts containing no oxygen, such as those containing Pt. Pd,Rh, Ru, Au, Ni, Cu, and Ag—Pd, since the mixing of the oxygen derivedfrom catalysts in the product can be prevented.

Furthermore, as the catalyst, it is possible to use the above-mentionedcatalysts which do not contain oxygen carried on the above-mentionedmetal oxides.

As the trap 328, it is possible to use an adsorption trap, a cold trap,or the like.

In using the isotope scrambler 300 shown herein, first, the vapor output(hereinafter, referred to as the enriched material) from thedistillation column in an earlier step is input, via the conduit pipe301, into the suction side of a circulatory blower 315, and is furtherintroduced into a catalytic column 302 via the conduit pipes 305 and306. In addition, the hydrogen produced in the electrolysis processdescribed in the following is supplied into the catalytic column 302 viathe conduit pipes 304 and 306. Additionally, hydrogen supplied from asupply source (not shown in the figures) may be supplied, via theconduit pipes 303 and 306, into the catalytic column 302, in accordancewith necessity.

The amount of hydrogen supplied to the catalytic column 302 isappropriately determined according to the flow rate of theaforementioned enriched material as measured by means of a flow meter(not shown in the figures) provided in conduit pipe 301.

The amount of hydrogen supplied is regulated by means of opening/closingregulating valves provided in conduit pipes 303 and 304, which arecontrolled by a control unit (not shown in the figures).

Simultaneously, diluent gas is introduced into the catalytic column 302via a conduit pipe 305 from conduit pipes 314 and 316. The diluent gasreduces the concentration of components in the vapor introduced into thecatalytic column 302 to a level no greater than that of the explosivelimits value, and maintains a low temperature within the catalyticcolumn 302 (for example, 150° C. or lower, and preferably 100° C. orlower). As the diluent gas, it is possible to use inert gases such asargon or the like.

The amount of the diluent gas supplied from the conduit pipe 316 isappropriately determined in accordance with the concentration,temperature, and the like of the component vapors introduced into thecatalytic column 302.

The aforementioned enriched material which is introduced into thecatalytic column 302 via the conduit pipe 301 reacts with hydrogenintroduced via the conduit pipe 303 and thereby water is produced.

Water vapor (produced water) produced in the catalytic column 302 isintroduced, via the conduit pipe 307, into the cooler 308, where thewater vapor is cooled and condensed by means of a “chiller” suppliedfrom a freezer 309, and then passes through the conduit pipe 310, and isstored in the water storage tanks 311 a and 311 b. Cooling of theproduced water preferably continues until the temperature of theproduced water decreases to 10° C. or below.

On the other hand, the cooler 308 comprises a heat exchange chamber anda condensed water separation chamber. The diluent gas separated from theproduced water in the condensed water separation chamber passes throughthe conduit pipes 312 and 314, and is reused by being returned to thecatalytic column 303 via the aforementioned conduit pipes 305 and 306 bymeans of the circulatory blower 315. Additionally, diluent gas may alsobe supplied into the conduit pipe 305 via the conduit pipe 316, ifnecessary.

The produced water stored in the water storage tanks 311 a and 311 b isintroduced, via the conduit pipe 317, into the electrolysis unit 320 forelectrolysis. In the electrolysis unit 320, oxygen is produced as aseparate product in the anode chamber 320 a, and hydrogen is produced asa separate product in the cathode chamber 320 b.

Hydrogen output from the cathode chamber 320 b is cooled in the cooler321, and is introduced into the catalytic column 302 via theaforementioned conduit pipes 304 and 306 by means of the circulatoryblower 322. The hydrogen introduced into the catalytic column 302 isrecycle and used as the hydrogen added to the above-mentioned enrichedmaterial.

Oxygen output from the anode chamber 320 a passes through conduit pipe323, and is cooled in the cooler 324 and after its pressure is raised bymeans of the blower 326, is introduced into the oxygen purifier 327.

In the oxygen purifier 327, impurities such as hydrogen and carbonmonoxide in the oxygen output from the anode chamber 320 a are oxidizedto form water, carbon dioxide and the like. The temperature in theoxygen purifier 327 is preferably set to approximately 300° C.

The impurities oxidized in the oxygen purifier 327 are removed by meansof the trap 328.

The oxygen having passed through the trap 328 is introduced, via aconduit pipe 329, into the distillation column located one step afterthis isotope scrambler 300.

If water vapor is mixed in with the hydrogen produced in the cathodechamber 320 b, the water vapor is cooled and condensed by means of thechiller supplied from the above-mentioned freezer 309 within the cooler321, and returned to the electrolysis unit 320.

If water vapor is mixed in with the oxygen produced in the anode chamber320 a, the water vapor is cooled and condensed by means of the chillersupplied from the above-mentioned freezer 309 within the cooler 324, andis returned to the electrolysis unit 320, via the conduit pipe 325.

In the method according to this embodiment, by means of reacting theaforementioned enriched material with hydrogen in the catalytic column302 to temporarily form water, the number of oxygen atoms contained permolecule equals one. In other words, the enriched material is reformedto simple oxygen in the electrolysis chamber 320 after separating oxygenout into single atoms. Accordingly, the aforementioned isotopescrambling (i.e., isotope exchange) is reliably conducted, and theconcentration of each component does reliably reach the values shown inthe above-mentioned formulae (i)˜(vi).

Thus, the concentration of heavy isotope oxygen molecules can bereliably increased.

In addition, the method of this embodiment is one in which the enrichedmaterial is temporarily formed into water, and this water is thenelectrolyzed. Since reaction rates for the production reaction for thiswater and the electrolysis of the water are high, it is possible toincrease production efficiency.

When the aforementioned electrolysis unit 320 is able to produce oxygenand hydrogen vapor of a high pressure in the anode chamber 320 a and thecathode chamber 320 b, the blowers 322 and 326 are not needed.

According to the aforementioned method, water is produced by means ofdiluting the enriched material with a diluent gas, and subsequentlyreacting the resultant material with hydrogen by means of employing acatalytic reaction. However, the present invention is not limited to theaforementioned, and it is possible to produce water by means ofcombusting the aforementioned hydrogen in the presence of theaforementioned enriched material, using a combustion chamber.

FIG. 20 shows the main aspects of an example of an isotope scramblerwherein water is produced by means of reacting the aforementionedenriched material with hydrogen using a combustion chamber.

The isotope scrambler 400 shown here comprises a buffer tank 341 fortemporarily storing the enriched material (oxygen vapor) which haspassed through the distillation column at an earlier step; a conduitpipe 342 for introducing the oxygen vapor into the buffer tank 341; aconduit pipe 343 for introducing hydrogen (containing deuterium)supplied from a supply source (not shown in the figure); a combustionchamber 344 for reacting the oxygen and hydrogen supplied from theconduit pipes 342 and 343; and a combustion chamber 401 having acontroller 345.

In the stage after the combustion chamber 401, water storage tanks 311 aand 311 b, a cooler 321, an electrolysis unit 320, a cooler 324, anoxygen purifier 327, and a trap 328, all of which are similar to thoseshown in FIG. 19, are provided.

The combustion chamber 344 comprises a burner 344 a for mixing andcombusting oxygen and hydrogen supplied into the combustion chamber 344;a heater 344 b for igniting the oxygen-hydrogen mixed vapor; and acooling coil 344 c for cooling the reactant product (i.e., water vapor).Additionally, a discharge opening 344 d is provided for expelling thereactant product (water) in the combustion chamber 344 via a valve.

The controller 345 regulates a flow regulating valve 342 b by means ofsignals based on the flow rate of oxygen vapor measured by an oxygenflow rate detector 342 a provided in conduit pipe 342, and thereby thecontroller 345 is able to adjust the supply volume of oxygen vaporsupplied into the combustion chamber 344 via the conduit pipe 342.

In addition, the controller 345 regulates a flow regulating valve 343 bby means of signals based on the flow rate of hydrogen which is measuredby a hydrogen flow rate detector 343 a provided in the conduit pipe 343,and thereby the controller 345 is able to adjust the supply volume ofhydrogen supplied into the combustion chamber 344 via the conduit pipe343.

Further, references 342 c and 343 c indicate check valves; references342 d and 343 d indicate back-fire prevention chambers; and reference344 e indicates a conduit pipe for discharging the small amount ofunreacted vapor remaining in the combustion chamber 344, via a valve.

In the following, an enrichment method is explained wherein theaforementioned isotope scrambler 400 is used instead of theaforementioned isotope exchanger 203 and/or isotope exchanger 207.

The output vapor which was output from the distillation column locatedat an earlier stage is introduced into the combustor 401 of the isotopescrambler 400 via the conduit pipe 330 and the regulating valve 330 a.

The oxygen vapor introduced into the combustor 401 passes through thebuffer tank 341, and is introduced into the combustion chamber 344 viathe conduit pipe 342.

Simultaneously, hydrogen supplied from a supply source not shown in thefigures is supplied to the combustion chamber 344 via the conduit pipe343.

At this point, the controller 345 performs a calculation based on signalbased on a predetermined value and a feedback signal based on the flowrate of oxygen vapor measured by the oxygen flow rate detector 342 a.The controller regulates the flow rate regulating valve 342 b by meansof a signal resulting from this calculation. In the same manner,controller 345 performs a calculation based on the signal based on apredetermined value and a feedback signal based on the flow rate ofhydrogen measured by the hydrogen flow rate detector 343 a. Thecontroller regulates the flow rate regulating valve 343 b by means of asignal resulting from this calculation. As a result, the aforementionedoxygen and hydrogen are supplied into the combustion chamber 244 involumes which approximate the stoichiometric volume for producing water.

The oxygen and hydrogen supplied to the combustion chamber 344 arealways regulated to a volume which closely approximates theaforementioned stoichiometric volume by means of the aforementionedfeedback control. However, despite this, excess supplied vapor isregularly discharged via a valve from a discharge conduit pipe 344 e,and this prevents the vapor from accumulating in the combustion chamber344.

In order to further reduce the volume of the exhaust vapor, it ispreferable to jointly employ an even more precise controlling means,such as a feed-forward controlling method.

The aforementioned oxygen and hydrogen supplied into the combustionchamber 344 are mixed by means of the burner 344 a, and subsequently,jetted into the combustion chamber 344, ignited by means of the heater344 b, and reacted with each other to produce water.

Most of the produced water is condensed by the cooling coil 344 c, andsubsequently expelled out of the combustion chamber 344 via thedischarge opening 344 d, and supplied, via the aforementioned conduitpipe 331, to the water storage tank 311 a or 311 b for storage.

The produced water output from the water storage tanks 311 a and 311 bis then sent to the electrolysis unit 320, and thereafter, isotopescrambling is conducted in the same manner as in the process using theisotope scrambler 300 shown in the aforementioned FIG. 19.

The aforementioned method for using a combustion chamber 401 does notcomprise a circulatory system for diluent gas, and thus leads to asimpler apparatus, compared to the method in which an isotope scrambler300 is employed.

Furthermore, the hydrogen supplied to the combustion chamber 401 isrecirculated and reused in the same manner as in the aforementionedmethod in which an isotope scrambler 300 is employed.

In addition, isotope scrambling may be conducted according to ahigh-heat thermal treatment method. In that case, the aforementionedisotope scrambling (i.e., isotope exchange) is conducted by means ofdirecting! the aforementioned enriched material into a silica pipeheated to 1000° C. or higher for thermal treatment.

Furthermore, isotope scrambling may be conducted by means of utilizingan oxidation-reduction reaction. In that method, the oxidation-reductionreaction is controlled by means of suitably setting condition such asthe partial pressure of oxygen and the reaction temperature during theoxidation-reduction reaction.

In this method, the enriched material (O₂) is reacted with an oxidizablematerial, such as a metal or metal oxide, to form a temporary oxide,which is subsequently reduced to produce oxygen. Thereby, isotopescrambling is carried out.

For example, oxygen is produced by means of reacting an oxidizablematerial such as a metal or oxides (e.g., Mn₃O₄, Ag, and Au) with theaforementioned enriched material according to one of the followingformulae to form an oxide (MnO₂, Ag₂O, Au₂O₃) and subsequently reducingthis oxide.

Mn₃O₄+O₂=3MnO₂

4Ag+O₂=2Ag₂O

4Au+3O₂=2Au₂O₃

In addition, a method may be employed in which oxygen is produced bymeans of reacting the aforementioned enriched material with Cu₂O, FeO,or CO as the oxidizable material (in the following way), to obtain anoxide (such as CuO, Fe₂O₃, and CO₂), and then subsequently reducing thisoxide.

Cu₂O+0.5O₂=2CuO

2FeO+2O₂=2Fe₂O₃

CO+0.5O₂=CO₂

Furthermore, an oxidization-reduction reaction using a peroxide (BaO₂)in the following manner may also be employed.

BaO+0.5O₂=BaO₂

In the aforementioned reaction, the equilibrium pressure for oxygendiffers depending on the temperature. For example, the reaction proceedsfrom left to right at a temperature of approximately 650° C., and thereaction proceeds from the right to left at a temperature ofapproximately 800° C.

In this case, by means of controlling the reaction by setting thetemperature and oxygen pressure at appropriate values, it is possible toutilize either reaction proceeding from left to right, or from right toleft.

In addition, as the above-mentioned oxidizable materials, in addition toBaO, SrO, CaO, a mixture of thereof, and the like may be used.

In addition, as the above-mentioned oxidizable materials, it is possibleto use a mixture of two or more of BaO, SrO, CaO, Cu2O, FeO, CO, Mn3O4,Ag, and Au.

In this way, after the oxidation of the oxidizable material by means ofthe heavy a oxygen isotope enriched material, the obtained oxideundergoes isotopic scrambling by means of reduction, and it is possibleto increase the rate of the reaction and production efficiency. Inaddition, isotope scrambling may be conducted by means of generatingoxygen plasma through silent discharge, high-frequency discharge, orelectromagnetic induction. In this method, an oxygen ion or radical isgenerated by means of the plasma, and as a result, isotope scrambling(i.e., isotope exchange) occurs between oxygen molecules and otheroxygen molecules in the enriched material.

In addition, a method may also be employed in which isotope scramblingis conducted by means of temporarily converting a portion of theenriched material to ozone, which is subsequently decomposed intooxygen. Preferred examples of the aforementioned method for ozonizationinclude irradiation with ultraviolet rays, and silent discharge.

In the oxygen isotope enrichment method according to the presentinvention, the output vapor 215 from the second distillation column 202may be directly supplied to the third distillation column 204 or fourthdistillation column 205, when conducting the enrichment of heavy oxygenisotopes by means of using the apparatus shown in FIG. 17 or 18.

Moreover, the present embodiment is not limited to situations ofenrichment of all the oxygen molecules (¹⁶O¹⁶O, ¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O,¹⁷O¹⁸O, and ¹⁸O¹⁸O) which contain heavy oxygen isotopes, and enrichmentof at least one of these six molecules is also possible

In the following, an explanation will be given of the results ofcomputer simulations conducted for situations in which the enrichment ofheavy oxygen isotopes was carried out using the apparatuses shown inFIGS. 17 and 18.

In these simulations, the above-mentioned rate model will be employed.

Embodiment 2

Tables 10 to 12 and FIGS. 21 to 23 show the simulation results, obtainedaccording to the aforementioned model, for a situation in which theprocesses for the apparatus shown in FIG. 17 are performed. Theconfiguration of the apparatus is shown in Table 9.

Tables 10 to 12 show the pressure, flow rate, and concentration ofisotopes for the vapor or liquid obtained in each process.

FIGS. 21 to 23 show the concentration distribution of each isotope inthe first through third distillation columns 201, 202, and 204.

In this simulation, the oxygen was taken to consist of six isotopes(¹⁶O¹⁶O, ¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O, :¹⁷O¹⁸O, and ¹⁸O¹⁸O).

TABLE 9 Embodiment 2 First Second Third distillation distillationdistillation column column column Specific surface area of packing 500500 500 (m²/m³) Inner diameter of distillation 1.780 0.290 0.125 column(m) Distance from the top of the column 70 100 80 to feed position (m)Height of packing (m) 300 300 400 Heat exchange amount of 1900 52 9reboiler/condenser (kW) Pressure (bar) 1.1˜1.7 1.1˜1.8 1.1˜2.0Superficial F factor [m/s (kg/m³)^(1/2)] 1.4˜1.6 1.5˜1.6 1.4˜1.6 (Heightof packing does not include the height of liquid collector and liquiddistributor.)

TABLE 10 Embodiment 2 First column First column First column outputexhaust feed 211 vapor 212 vapor 213 Pressure (bar) 1.2 1.7 1.1 Flowrate (mol/s) 1.000 0.0148 0.997 Concentration of ¹⁶O¹⁶O (-) 0.995 0.7770.998 Concentration of ¹⁶O¹⁷O (-) 7.38 × 10⁻⁴ 9.68 × 10⁻³ 6.86 × 10⁻⁴Concentration of ¹⁶O¹⁸O (-) 4.07 × 10⁻³ 0.213 1.32 × 10⁻³ Concentrationof ¹⁷O¹⁷O (-) 1.37 × 10⁻⁷ 9.23 × 10⁻⁶ 5.02 × 10⁻⁸ Concentration of¹⁷O¹⁸O (-) 1.51 × 10⁻⁶ 1.15 × 10⁻⁴ 1.28 × 10⁻⁷ Concentration of ¹⁸O¹⁸O(-) 4.16 × 10⁻⁶ 3.23 × 10⁻⁴ 1.24 × 10⁻⁷ (First column: Firstdistillation column 201)

TABLE 11 Embodiment 2 Second Second Second column column column outputreturned feed 214 vapor 215 vapor 216 Pressure (bar) 1.3 1.8 1.1 Flowrate (mol/s) 0.0148 2.95 × 10⁻³ 0.0118 Concentration of ¹⁶O¹⁶O (-) 0.7890.106 0.960 Concentration of ¹⁶O¹⁷O (-) 8.72 × 10⁻³ 0.0137 7.49 × 10⁻³Concentration of ¹⁶O¹⁸O (-) 0.190 0.818 0.0328 Concentration of ¹⁷O¹⁷O(-) 2.41 × 10⁻⁵ 1.04 × 10⁻⁴ 4.18 × 10⁻⁶ Concentration of ¹⁷O¹⁸O (-) 1.05× 10⁻³ 5.14 × 10⁻³ 2.65 × 10⁻⁵ Concentration of ¹⁸O¹⁸O (-) 0.0114 0.05696.20 × 10⁻⁵ (Second column: Second distillation column 202)

TABLE 12 Embodiment 2 Third Third Third column column column feed outputexhaust 217 vapor 218 vapor 219 Pressure (bar) 1.3 2.0 1.1 Flow rate(mol/s) 2.95 × 10⁻³ 4.72 × 10⁻⁴ 2.48 × 10⁻³ Concentration of ¹⁶O¹⁶O (-)0.272 5.87 × 10⁻⁶ 0.324 Concentration of ¹⁶O¹⁷O (-) 9.92 × 10⁻³ 2.08 ×10⁻⁴ 0.0118 Concentration of ¹⁶O¹⁸O (-) 0.489 5.17 × 10⁻³ 0.581Concentration of ¹⁷O¹⁷O (-) 9.03 × 10⁻⁵ 9.49 × 10⁻⁷ 1.07 × 10⁻⁴Concentration of ¹⁷O¹⁸O (-) 8.91 × 10⁻³ 4.08 × 10⁻³ 9.83 × 10⁻³Concentration of ¹⁸O¹⁸O (-) 0.220 0.991 0.0729 (Third column: Thirddistillation column 204)

Embodiment 3

Tables 14 to 18 and FIGS. 24 to 27 show the simulation results, usingthe aforementioned model, for a situation in which the processes for theapparatus shown in FIG. 18 are performed.

Table 13 shows the configuration, heat exchange amount of thereboiler/condenser, operating pressure, and superficial F factor of eachdistillation column.

Tables 14 to 17 show the pressure, flow rate, and concentration of theisotopes for the vapor or liquid obtained in each process.

Table 18 shows the composition of the vapor output from the fourthdistillation column 205, in addition to the pressure, flow rate, andcomposition concentration of the finished product vapor output from eachof the top of the column and the bottom of the column. Table 18 showsthe atomic ratio of the product obtained in the fourth distillationcolumn 205.

FIGS. 24 to 27 show the concentration distribution of each isotopewithin each of the first through fourth distillation columns 201, 202,204, and 205.

TABLE 13 Embodiment 1 First Second Third Fourth distillationdistillation distillation distillation column Column column columnSpecific surface area of 500 500 500 500 packing (m²/m³) Inner diameterof 1.780 0.290 0.125 0.092 distillation column (m) Distance from the topof 70 100 100 200 the column to the feed position (m) Height of packing(m) 300 300 600 200 Heat exchange amount 1900 52 12 6 ofreboiler/condenser (kW) Pressure (bar) 1.1˜1.7 1.1˜1.8 1.1˜3.0 1.1˜2.3Superficial F factor 1.4˜1.6 1.5˜1.7 1.6˜2.1 1.6˜2.0 [m/s (kg/m³)^(1/2)](Height of packing does not include the height of liquid collector, andliquid distributor.)

TABLE 14 Embodiment 3 First column First column First column outputexhaust feed 211 vapor 212 vapor 213 Pressure (bar) 1.2 1.7 1.1 Flowrate (mol/s) 1.000 0.0148 0.999 Concentration of ¹⁶O¹⁶O (-) 0.995 0.6140.997 Concentration of ¹⁶O¹⁷O (-) 7.38 × 10⁻⁴ 8.37 × 10⁻³ 7.29 × 10⁻⁴Concentration of ¹⁶O¹⁸O (-) 4.07 × 10⁻³ 0.376 2.10 × 10⁻³ Concentrationof ¹⁷O¹⁷O (-) 1.37 × 10⁻⁷ 1.87 × 10⁻⁶ 9.32 × 10⁻⁸ Concentration of¹⁷O¹⁸O (-) 1.51 × 10⁻⁶ 3.37 × 10⁻⁴ 1.85 × 10⁻⁷ Concentration of ¹⁸O¹⁸O(-) 4.16 × 10⁻⁴ 9.94 × 10⁻⁴ 1.37 × 10⁻⁷ (First column: Firstdistillation column 201)

TABLE 15 Embodiment 3 Second Second Second column column column outputexhaust feed 214 vapor 215 vapor 216 Pressure (bar) 1.3 1.8 1.1 Flowrate (mol/s) 0.0148 2.95 × 10⁻³ 0.0138 Concentration of ¹⁶O¹⁶O (-) 0.6500.0114 0.731 Concentration of ¹⁶O¹⁷O (-) 7.05 × 10⁻³ 8.37 × 10⁻³ 8.25 ×10⁻³ Concentration of ¹⁶O¹⁸O (-) 0.305 0.709 0.260 Concentration of¹⁷O¹⁷O (-) 1.91 × 10⁻⁵ 5.21 × 10⁻⁵ 1.69 × 10⁻⁵ Concentration of ¹⁷O¹⁸O(-) 1.65 × 10⁻³ 0.0102 2.66 × 10⁻⁴ Concentraiion of ¹⁸O¹⁸O (-) 0.03580.187 7.74 × 10⁻⁴ (Second column: Second distillation column 202)

TABLE 16 Embodiment 3 Third Third Third column column column outputexhaust feed 217 vapor 218 vapor 219 Pressure (bar) 1.4 3.0 1.1 Flowrate (mol/s) 2.95 × 10⁻³ 1.00 × 10⁻³ 1.95 × 10⁻³ Concentration of ¹⁶O¹⁶O(-) 0.166 1.18 × 10⁻⁵ 0.251 Concentration of ¹⁶O¹⁷O (-) 4.86 × 10⁻³ 3.87× 10⁻⁷ 7.37 × 10⁻³ Concentration of ¹⁶O¹⁸O (-) 0.478 9.91 × 10⁻³ 0.719Concentration of ¹⁷O¹⁷O (-) 3.56 × 10⁻⁵ 7.34 × 10⁻⁷ 5.36 × 10⁻⁵Concentration of ¹⁷O¹⁸O (-) 7.01 × 10⁻³ 0.0114 4.73 × 10⁻³ Concentraiionof ¹⁸O¹⁸O (-) 0.344 0.979 0.0176 (Third column: Third distillationcolumn 204)

TABLE 17 Embodiment 3 Fourth column Fourth output vapor column Fourth209 from output vapor column bottom of 210 from top feed 218 column ofcolumn Pressure (bar) 3.0 2.3 1.1 Flow rate (mol/s) 1.00 × 10⁻³ 9.34 ×10⁻⁴ 7.03 × 10⁻⁵ Concentration of ¹⁶O¹⁶O (-) 1.18 × 10⁻⁵ 1.49 × 10⁻³1.69 × 10⁻⁴ Concentration of ¹⁶O¹⁷O (-) 3.87 × 10⁻⁷  5.09 × 10⁻¹⁰ 5.52 ×10⁻⁶ Concentration of ¹⁶O¹⁸O (-) 9.91 × 10⁻³ 2.13 × 10⁻³ 0.139Concentration of ¹⁷O¹⁷O (-) 7.34 × 10⁻⁷ 1.58 × 10⁻⁸ 1.03 × 10⁻⁵Concentration of ¹⁷O¹⁸O (-) 0.0114 4.53 × 10⁻³ 0.103 Concentraiion of¹⁸O¹⁸O (-) 0.979 0.995 0.758 (Fourth column: Fourth distillation column205)

TABLE 18 Embodiment 3 Fourth column output Fourth column output vapor209 from vapor 210 from First column bottom of column top of column feed211 Atomic ratio Yield Atomic ratio Yield Flow rate (mol/s) 1.000Concentration of ¹⁶O (-) 0.99759 0.000107 9.97 × 10⁻⁸ 0.069670 4.91 ×10⁻⁶ Concentration of ¹⁷O (-) 0.00037 0.002265 5.72 × 10⁻³ 0.051513 9.79× 10⁻³ Concentration of ¹⁸O (-) 0.00204 0.997628 4.57 × 10⁻¹ 0.8788173.03 × 10⁻²

As shown in FIG. 26, a peak in the concentration of ¹⁷O¹⁸O appears inthe middle section of the third distillation column 204.

Comparative Embodiment 1

For the purpose of comparison, Tables 19 and 20 show the results of acomputer simulation using the aforementioned: model for a situation inwhich enrichment of heavy oxygen isotopes is attempted withoutconducting isotope exchange.

In this embodiment, it is assumed that the same apparatus as the oneshown in FIG. 16 is used with the exception that an isotope exchanger203 is not provided. The configuration of the apparatus was determinedaccording to Embodiment 2 (Table 9).

TABLE 19 Comparative Embodiment 1 First First column First column columnoutput exhaust feed 211 vapor 212 vapor 213 Pressure (bar) 1.2 1.7 1.1Flow rate (mol/s) 1.000 0.0148 0.997 Concentration of ¹⁶O¹⁶O (-) 0.9950.764 0.998 Concentration of ¹⁶O¹⁷O (-) 7.38 × 10⁻⁴ 0.0101 7.06 × 10⁻⁴Concentration of ¹⁶O¹⁸O (-) 4.07 × 10⁻³ 0.226 1.36 × 10⁻³ Concentrationof ¹⁷O¹⁷O (-) 1.37 × 10⁻⁷ 7.60 × 10⁻⁶ 4.58 × 10⁻⁸ Concentration of¹⁷O¹⁸O (-) 1.51 × 10⁻⁶ 9.63 × 10⁻⁵ 1.26 × 10⁻⁷ Concentration of ¹⁸O¹⁸O(-) 4.16 × 10⁻⁶ 2.75 × 10⁻⁴ 1.24 × 10⁻⁷ (First column: Firstdistillation column 201)

TABLE 20 Comparative Embodiment 1 Second Second Second column columncolumn output returned feed 214 vapor 215 vapor 216 Pressure (bar) 1.31.8 1.1 Flow rate (mol/s) 0.0148 2.95 × 10⁻³ 0.0118 Concentration of¹⁶O¹⁶O (-) 0.764 0.0672 0.938 Concentration of ¹⁶O¹⁷O (-) 0.0101 0.01179.67 × 10⁻³ Concentration of ¹⁶O¹⁸O (-) 0.226 0.919 0.0527 Concentrationof ¹⁷O¹⁷O (-) 7.60 × 10⁻⁶ 3.09 × 10⁻⁵ 1.77 × 10⁻⁶ Concentration of¹⁷O¹⁸O (-) 9.63 × 10⁻⁵ 4.69 × 10⁻⁴ 3.08 × 10⁻⁶ Concentration of ¹⁸O¹⁸O(-) 2.75 × 10⁻⁴ 1.37 × 10⁻³ 1.77 × 10⁻⁶ (Second column: Seconddistillation column 202)

Comparative Embodiment 2

The results (the concentration distribution of isotopes within thedistillation column) for a situation in which enrichment of isotopes ofan oxygen starting material was attempted using a single distillationcolumn are shown in FIG. 8.

From Tables 10 to 12 and FIGS. 21 to 23, it is clear that an enrichedmaterial with a concentration of the heavy isotope oxygen molecule¹⁸O¹⁸O of at least 99% can be obtained as the output vapor 218 of thethird distillation column 204 in Embodiment 2 in which the use of theapparatus shown in FIG. 17 was assumed.

Additionally, when comparing the output vapor 215 from the seconddistillation column obtained in a situation in which isotope exchangewas conducted (Table 11) and the enriched material obtained inComparative Embodiment 1 and Comparative Embodiment 2 in which isotopeexchange was not conducted, it is clear that the concentration of heavyoxygen isotopes, ¹⁸O¹⁸O in particular, can be increased by means ofisotope exchange.

In addition, from Tables 14 and 18 and FIGS. 24 and 27, it is clear thatit is possible to obtain an enriched material with a concentration of¹⁸O¹⁸O of 99.5% as output vapor 209 from the bottom of the fourthdistillation column 205 in Embodiment 3, in which it is assumed that thedistillation is performed such that a peak in the concentration of¹⁷O¹⁸O occurs in the middle section of the third distillation column204, using the apparatus shown in FIG. 18.

Additionally, it is shown that the yield of ¹⁸O¹⁸O, which is determinedby the flow rate (9.34×10⁻⁴ mol/s) of the output vapor 209 from thebottom of the column, is a sufficiently high value of 47.5%, andtherefore it is possible to recover ¹⁸O¹⁸O at a high yield.

The production rate of the aforementioned ¹⁸O¹⁸O (with a purity of99.5%) is equivalent to approximately 1,000 kg per year, and it is clearthat it is possible to obtain a production volume which is sufficientfor the purpose of industrial production.

Additionally, in Embodiment 3, an enriched material comprising ¹⁷O¹⁸O ata concentration of 10% or greater can be obtained as the output vapor210 from the top of the column.

According to the method of Embodiment 3, the enrichment rate for ¹⁷O canbe remarkably increased, whereas the enrichment rate of H₂ ¹⁷O islimited to 1% to 3% in enrichment-separation of H₂ ¹⁷O according toconventional water distillation methods.

When the flow rate of the output vapor 209 is 7.03×10⁻⁵ mol/s and theconcentration of ¹⁷O¹⁸O is 10.3%, a sufficiently high value, it ispossible to recover ¹⁷O¹⁸O at a high yield.

The production rate of the aforementioned ¹⁷O¹⁸O (with a purity of10.3%) is equivalent to approximately 77.5 kg per year, and it is clearthat it is possible to obtain a production rate which is sufficient forthe purpose of industrial production.

As explained above, by means of the present invention, it is possible toobtain the effects shown below.

(1) Since oxygen which does not contain other elements is used as thestarting material, it is possible to obtain an enriched product with ahigh concentration of heavy oxygen isotopes.

(2) Since the latent heat of vaporization of oxygen (the startingmaterial) is low, it is possible to reduce the size of the distillationcolumns, the heat exchangers, and the like compared with those for waterdistillation methods, and thus it is possible to reduce apparatus costsand operation costs.

(3) Since the oxygen starting material is not a corrosive or toxic gas,it is advantageous with regard to ease of handling and safety.

(4) By means of the use of a distillation column in which structuredpacking is used, it is possible to reduce liquid hold-up, and thus it ispossible to shorten the time required to start up the apparatus.Furthermore, it is possible to reduce operating costs associatedtherewith.

(5) By means of using structured packing, it is possible to increase theefficiency of vapor-liquid contact within the distillation column, andthereby it is possible to increase the efficiency of the isotopeenrichment.

(6) By means of using structured packing, the pressure loss for which islow, it is possible to carry out the distillation under conditions inwhich the relative volatility of each component is comparatively largeand thereby it is possible to increase the efficiency of the enrichmentof oxygen molecules containing heavy isotopes.

(7) By means of using promoting-fluid-dispersion type structured packingas the structured packing, it is possible to increase the efficiency ofvapor-liquid contact, and thereby it is possible to further increase theefficiency of the enrichment of heavy oxygen isotopes.

(8) By means of the provision of a condenser and a reboiler in thedistillation column, and by using and circulating a medium for heatexchange between the condenser and the reboiler, it is possible to makeuse of the coolness of the medium for heat exchange without waste, tosuppress energy loss to a minimum and thereby to reduce operating costs.

(9) By means of the use of a plurality of distillation columns, it ispossible to obtain an enriched product for which the ratio of enrichmentis even higher. In addition, it is possible to reduce the height of thedistillation columns, and to make the construction of the apparatus as awhole compact.

(10) After the enrichment of an oxygen starting material in oxygenmolecules containing heavy oxygen isotopes (¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O,¹⁷O¹⁸O, and ¹⁸O¹⁸O) by means of the cryogenic distillation of an oxygenstarting material which contains heavy oxygen isotopes, theconcentration of heavy isotope oxygen molecules (¹⁸O¹⁸O, ¹⁷O¹⁸O, and¹⁷O¹⁷O which are oxygen molecules which comprise only heavy isotopes)within the enriched material is increased by means of isotope exchange,and thereby it is possible to obtain a finished product containing ahigh concentration of heavy oxygen isotopes.

(11) It is possible to increase the production efficiency and toincrease the rate of the reaction by means of the carrying out theisotope scrambling by adding hydrogen to the enriched material (enrichedin heavy oxygen isotopes) and causing them to react to produce watercontaining a high concentration of the heavy oxygen isotopes, and thenseparating this produced water into hydrogen and oxygen containing heavyoxygen isotopes by means of electrolysis.

(12) It is possible to increase the production efficiency and toincrease the rate of the reaction by means of conducting isotopescrambling by means of oxidizing an oxidizable material by means of sdwith the enriched material containing heavy oxygen isotopes, andsubsequently reducing the obtained oxide.

Industrial Applicability

The method and apparatus for enrichment of heavy oxygen isotopes of thepresent invention can be used for enrichment of ¹⁷O and ¹⁸O which arethe heavy oxygen isotopes used as tracers and the like.

What is claimed is:
 1. A method of enrichment of heavy oxygen isotopescomprising: enriching an oxygen starting material containing heavyoxygen isotopes in at least one of oxygen molecules selected from thegroup consisting of ¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O, ¹⁷O¹⁸O and ¹⁸O¹⁸O by meansof cryogenic distillation; conducting isotope scrambling; and obtainingan enriched material containing a high concentration of at least one ofsaid oxygen molecules containing said heavy oxygen isotopes.
 2. A methodof enrichment of heavy oxygen isotopes according to claim 1, wherein anenriched material containing a high concentration of at least one ofsaid oxygen molecules containing said heavy oxygen isotopes is obtainedby means of conducting further cryogenic distillation on a heavy oxygenisotope enriched material obtained by means of said isotope scrambling.3. A method of enrichment of heavy oxygen isotopes wherein theconcentration of at least one component of a heavy oxygen isotopeenriched material, obtained by means of said method of enrichment ofheavy oxygen isotopes according to claim 2, is increased by means ofconducting additional isotope scrambling.
 4. A method of enrichment ofheavy oxygen isotopes, wherein the concentration of at least the heavyisotope oxygen ¹⁸O¹⁸O of a heavy oxygen isotope enriched material,obtained by means of said method of enrichment of heavy oxygen isotopesaccording to claim 3, is further increased by means of conductinganother cryogenic distillation.
 5. A method of enrichment of heavyoxygen isotopes wherein a heavy oxygen isotope enriched materialcontaining an increased concentration of the heavy isotope oxygen¹⁸O¹⁸O, and an enriched material containing an increased concentrationof the heavy oxygen isotope containing the heavy isotope oxygen ¹⁷O¹⁸Oare obtained by means of performing further cryogenic distillation of aheavy oxygen isotope enriched material obtained by means of a heavyoxygen isotope enrichment method according to any one of claims 2 and 4.6. A method of enrichment of heavy oxygen isotopes according to any oneof claims 1 and 3, wherein said isotope scrambling for concentratingheavy oxygen isotopes comprises isotope exchange using a catalyticreaction.
 7. A method of enrichment of heavy oxygen isotopes accordingto any one of claims 1 and 3, wherein said isotope scrambling forconcentrating heavy oxygen isotopes comprises: producing watercontaining a high concentration of said heavy oxygen isotopes by meansof adding and reacting hydrogen to said heavy oxygen isotope enrichedmaterial; and subsequently separating the hydrogen and oxygen containingheavy oxygen isotopes by means of conducting electrolysis on theproduced water.
 8. A method of enrichment of heavy oxygen isotopesaccording to claim 7, wherein said reaction between said enrichedmaterial and hydrogen is conducted by means of combustion using acombustion chamber.
 9. A method of enrichment of heavy oxygen isotopesaccording to claim 7, wherein said reaction between said enrichedmaterial and hydrogen is a catalytic reaction in which a diluent gas issupplied to said reaction system to dilute said enriched material andhydrogen.
 10. A method of enrichment of heavy oxygen isotopes accordingto claim 9, wherein water produced by means of reacting said enrichedmaterial with hydrogen and the diluent gas are cooled and condensed; themixture of produced water and the diluent gas are separated into thediluent gas and the condensed water; and said diluent gas is returned tosaid reaction system for recirculation and reuse.
 11. A method ofenrichment of heavy oxygen isotopes according to claim 7, whereinhydrogen produced by means of said electrolysis is recycled and reusedas said hydrogen added to said enriched material.
 12. A method ofenrichment of heavy oxygen isotopes according to claim 7, whereinimpurities in oxygen produced by means of said electrolysis are removedthrough oxidization by means of a catalytic reaction.
 13. A method ofenrichment of heavy oxygen isotopes according to any one of claims 1 and3, wherein said isotope scrambling for concentrating heavy oxygenisotopes comprises passing said heavy oxygen isotope enriched materialthrough plasma by means of silent discharge, high-frequency discharge,or electromagnetic induction.
 14. A method of enrichment of heavy oxygenisotopes according to any one of claims 1 and 3, wherein said isotopescrambling for concentrating heavy oxygen isotopes comprises:irradiating said heavy oxygen isotope enriched material with ultravioletrays to form ozone from said enriched material, and decomposing saidozone.
 15. A method of enrichment of heavy oxygen isotopes according toany one of claims 1 and 3, wherein said isotope scrambling forconcentrating heavy oxygen isotopes comprises: performing anoxidation-reduction reaction between said heavy oxygen isotope enrichedmaterial and a material selected from the group consisting of BaO, SrO,CaO, Cu₂O₃, FeO, CO, Mn₃O₄, Ag, Au, and/or a mixture thereof.
 16. Amethod of enrichment of heavy oxygen isotopes according to any one ofclaims 1 and 3, wherein said isotope scrambling for concentrating heavyoxygen isotopes comprises an isotope exchange in which said heavy oxygenisotope enriched material is thermally treated at a temperature of 1000°C. or higher.
 17. A method of enrichment of heavy oxygen isotopescomprising: supplying an oxygen starting material containing heavyoxygen isotopes to a distillation column packed with structured packing,said oxygen starting material being high purity oxygen obtained from ahigh purity oxygen preparation device using cryogenic distillation; andenriching said oxygen starting material containing heavy oxygen isotopesin at least one of oxygen molecules selected from the group consistingof ¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O, ¹⁷O¹⁸O and ¹⁸O¹⁸O, by means of cryogenicdistillation, wherein said distillation column comprises a condenser forcooling and liquefying a vapor output from said distillation column, anda reboiler for heating and vaporizing a liquid output from saiddistillation column, and a heating medium for exchanging heat with theoutput vapor and the output liquid in said condenser and said reboiler,said heating medium being circulated between said condenser and saidreboiler and being at least one gas selected from the group consistingof nitrogen, oxygen, air, and an exhaust gas emitted from an airliquefying and separating unit provided with said distillation column,the density corrected superficial velocity in said distillation columnis in the range between 0.8 and 1.8 m/s (kg/m³)^(½), and thedistillation pressure in said distillation column is in the rangebetween 1.1 and 2.5 bar.
 18. A method of enrichment of heavy oxygenisotopes according to claim 17, comprising: using a unit consisting of,as said distillation column, three distillation columns (a first column,a second column and a third column); supplying a starting materialoxygen to the interior of the first column from a feed section;supplying at least a part of liquid or vapor output from the bottom ofthe first column to the second column; supplying at least a part ofliquid or vapor output from the second column to the third column; andobtaining enriched vapor having a concentration of ¹⁶O¹⁷O of 10% orgreater from the top of the third column.
 19. A method of enrichment ofheavy oxygen isotopes according to claim 17, comprising: carrying outthe distillation in such a way that a concentration peak of ¹⁶O¹⁷O iscreated at the middle of the second column, and a mixture of heavyoxygen isotopes containing ¹⁶O¹⁷O at a concentration of 1% or greater,¹⁶O¹⁸O at a concentration of 90% or greater, and a remainder beingmostly ¹⁶O¹⁶O is obtained from the bottom of the second column.
 20. Amethod of enrichment of heavy oxygen isotopes according to claim 17,comprising: carrying out the distillation in such a way that enrichedliquid or vapor containing a concentration of ¹⁶O¹⁸O of 90% or greateris obtained from the bottom of the third column.
 21. A method ofenrichment of heavy oxygen isotopes according to claim 17 comprising:using a plurality of distillation columns; and operating said pluralityof distillation columns such that a maximum concentration of ¹⁷O¹⁸Oappears in the middle section within the penultimate distillationcolumn, when enriching in oxygen molecules containing heavy oxygenisotopes by means of performing said cryogenic distillation.
 22. Anapparatus for enrichment of heavy oxygen isotopes comprising: at leastone distillation column for enriching an oxygen starting materialcontaining heavy oxygen isotopes in at least one oxygen moleculeselected from the group consisting of ¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O, ¹⁷O¹⁸O and¹⁸O¹⁸O by means of cryogenic distillation; and at least one isotopescrambler for increasing the concentration of at least one oxygenmolecule selected from the group consisting of ¹⁶O¹⁷O, ¹⁶O¹⁸O, ¹⁷O¹⁷O,¹⁷O¹⁸O and ¹⁸O¹⁸O in a heavy oxygen isotope enriched material obtainedfrom said distillation column by means of isotope scrambling.
 23. Anapparatus for enrichment of heavy oxygen isotopes according to claim 22,wherein said isotope scrambler is provided with an isotope exchangecatalyst for promoting isotope exchange within said enriched material,and said isotope exchange catalyst contains at least one component ormixture thereof selected from the group consisting of tungsten,tantalum, palladium, rhodium, platinum, and gold.
 24. An apparatus forenrichment of heavy oxygen isotopes according to claim 22, wherein saidisotope scrambler is provided with an isotope exchange catalyst topromote isotope exchange of said enriched material, and said isotopeexchange catalyst contains at least one component or mixture thereofselected from the group consisting of Ti-oxide, Zr-oxide, Cr-oxide,Mn-oxide, Fe-oxide, Co-oxide, Ni-oxide, Cu-oxide, Al-oxide, Si-oxide,Sn-oxide, and V-oxide.
 25. An apparatus for enrichment of heavy oxygenisotopes according to claim 22, wherein the distillation column ispacked with structured packing, and said structured packing is apromoting-fluid-dispersion structured packing which has a structure suchthat when a liquid descending in the distillation column and a vaporascending in the distillation column make contact, the liquid and thevapor flow in mutually opposite directions over a surface of saidstructured packing along a main flow direction which is along adirection of a column axis, and, at the same time, mixing of the liquidand/or the vapor in a direction at right angles to said main flowdirection is promoted and mass transfer occurs.